drm/amd/display: Add null check for head_pipe in dcn201_acquire_free_pipe_for_layer

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "drivers/gpu/drm/amd/display/dc/resource/dcn201/dcn201_resource.c"
                    ],
                    "versions": [
                        {
                            "version": "4562236b3bc0a28aeb6ee93b2d8a849a4c4e1c7c",
                            "lessThan": "d11ae22a8beee9771d933c1e5c95e217edcdbd38",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "4562236b3bc0a28aeb6ee93b2d8a849a4c4e1c7c",
                            "lessThan": "16ce8fd94da8599bb6f0496895d392a69aead1c0",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "4562236b3bc0a28aeb6ee93b2d8a849a4c4e1c7c",
                            "lessThan": "390d757621f5f35d11a63ed7d9d3262ead240064",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "4562236b3bc0a28aeb6ee93b2d8a849a4c4e1c7c",
                            "lessThan": "8a1b1655a490a492a5a6987254c935ecce4eb9de",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "4562236b3bc0a28aeb6ee93b2d8a849a4c4e1c7c",
                            "lessThan": "f22f4754aaa47d8c59f166ba3042182859e5dff7",
                            "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/gpu/drm/amd/display/dc/resource/dcn201/dcn201_resource.c"
                    ],
                    "versions": [
                        {
                            "version": "4.15",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "4.15",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.1.191",
                            "lessThanOrEqual": "6.1.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.6.79",
                            "lessThanOrEqual": "6.6.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.10.14",
                            "lessThanOrEqual": "6.10.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.11.3",
                            "lessThanOrEqual": "6.11.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.12",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }