net: ravb: avoid dereferencing an invalid PTP clock

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "drivers/net/ethernet/renesas/ravb.h",
                        "drivers/net/ethernet/renesas/ravb_main.c",
                        "drivers/net/ethernet/renesas/ravb_ptp.c"
                    ],
                    "versions": [
                        {
                            "version": "a0d2f20650e81407d8e51ad2cbdc492861c74e9c",
                            "lessThan": "29ffd972531f8e6e0edf4ea3496190acff9fc9c2",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "a0d2f20650e81407d8e51ad2cbdc492861c74e9c",
                            "lessThan": "bf3308416a2be85dcc9965b614a745b40beeff14",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "a0d2f20650e81407d8e51ad2cbdc492861c74e9c",
                            "lessThan": "fc710f89a644e030a7ca15343176ca862fd61b9d",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "a0d2f20650e81407d8e51ad2cbdc492861c74e9c",
                            "lessThan": "8d4d06d6e2b501cb8e30ed3b1924c470358e8052",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "a0d2f20650e81407d8e51ad2cbdc492861c74e9c",
                            "lessThan": "0aaa53936419cf0c19c670387fc6d431e042a1b6",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "a0d2f20650e81407d8e51ad2cbdc492861c74e9c",
                            "lessThan": "1f77af0aaf277413ff32f6ff8c2c4282bd64c897",
                            "status": "affected",
                            "versionType": "git"
                        }
                    ]
                }

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "affected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "drivers/net/ethernet/renesas/ravb.h",
                        "drivers/net/ethernet/renesas/ravb_main.c",
                        "drivers/net/ethernet/renesas/ravb_ptp.c"
                    ],
                    "versions": [
                        {
                            "version": "4.2",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "4.2",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.1.188",
                            "lessThanOrEqual": "6.1.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.6.157",
                            "lessThanOrEqual": "6.6.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.12.109",
                            "lessThanOrEqual": "6.12.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.18.50",
                            "lessThanOrEqual": "6.18.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.2.4",
                            "lessThanOrEqual": "7.2.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.3",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }