nouveau: lock the client object tree.

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "drivers/gpu/drm/nouveau/include/nvkm/core/client.h",
                        "drivers/gpu/drm/nouveau/nvkm/core/client.c",
                        "drivers/gpu/drm/nouveau/nvkm/core/object.c"
                    ],
                    "versions": [
                        {
                            "version": "bf81df9be28657eea4aca8c6ab4ed3e69f8a051c",
                            "lessThan": "bc91f00112f944f3cb488f7f9266c8b4761157a6",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "bf81df9be28657eea4aca8c6ab4ed3e69f8a051c",
                            "lessThan": "6887314f5356389fc219b8152e951ac084a10ef7",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "bf81df9be28657eea4aca8c6ab4ed3e69f8a051c",
                            "lessThan": "96c8751844171af4b3898fee3857ee180586f589",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "bf81df9be28657eea4aca8c6ab4ed3e69f8a051c",
                            "lessThan": "b7cc4ff787a572edf2c55caeffaa88cd801eb135",
                            "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/nouveau/include/nvkm/core/client.h",
                        "drivers/gpu/drm/nouveau/nvkm/core/client.c",
                        "drivers/gpu/drm/nouveau/nvkm/core/object.c"
                    ],
                    "versions": [
                        {
                            "version": "4.3",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "4.3",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.1.191",
                            "lessThanOrEqual": "6.1.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.6.24",
                            "lessThanOrEqual": "6.6.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.7.12",
                            "lessThanOrEqual": "6.7.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.8",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }