drm/amdgpu: improve sa_bo->fence by kernel fence

Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian K?nig <christian.koenig@amd.com>
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index dd3415d..d7c02e1 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1042,7 +1042,7 @@
 	}
 
 	amdgpu_ring_unlock_commit(ring);
-	amdgpu_sync_free(adev, &sync, *fence);
+	amdgpu_sync_free(adev, &sync, &(*fence)->base);
 
 	return 0;
 }