drm/amdgpu: fix lost sync_to if scheduler is enabled.

commit 888c9e33e4c5a503285921046c621f7c73199d2f upstream.

when scheduler is enabled, the semaphore isn't used at all.

Signed-off-by: Chunming Zhou <David1.Zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>