drm/amdgpu: Do error injection even vram reserve fails

As long as the address is mapped with vram, we can do an error
injection.

Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>