drm/amdgpu: use the preferred pin domain after the check

For some reason we run into an use case where a BO is already pinned
into GTT, but should be pinned into VRAM|GTT again.

Handle that case gracefully as well.

Reviewed-by: Shashank Sharma <Shashank.sharma@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org