drm/amdgpu: fix a page fault

The UVD firmware is copied to cpu addr in uvd_resume, so it
should be used after that. This is to fix a bug introduced by
patch drm/amdgpu: fix SI UVD firmware validate resume fail.

Signed-off-by: Sonny Jiang <sonny.jiang@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
CC: stable@vger.kernel.org