drm/amdgpu: remove amdgpu_sync_wait

Stop hiding bugs, instead print a proper error when the scheduler
doesn't handle all dependencies.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>