drm/amdgpu: Fix possible null pointer dereference

stable inclusion
from stable-v6.6.3
commit 5e4d9fda7e65cd267900f7d2c7c1579a98bf413c
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8LBQP

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5e4d9fda7e65cd267900f7d2c7c1579a98bf413c



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commit 256503071c2de2b5b5c20e06654aa9a44f13aa62 upstream.

mem = bo->tbo.resource may be NULL in amdgpu_vm_bo_update.

Fixes: 18025378 ("drm/ttm: stop allocating dummy resources during BO creation")
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>