drm/amd/amdgpu: Check tbo resource pointer

[ Upstream commit 6cd2b872 ]

Validate tbo resource pointer, skip if NULL

Signed-off-by: Asad Kamal <asad.kamal@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>