drm/amdgpu: Drop deferred error in uncorrectable error check

Drop checking deferred error which can be handled by poison
consumption.

Signed-off-by: Candice Li <candice.li@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>