drm/vmwgfx: Free user-space fence objects correctly

They need to be freed after an rcu grace period.
Signed-off-by: NThomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/vmwgfx/vmwgfx_fence.c

@@ -537,7 +537,7 @@ static void vmw_user_fence_destroy(struct vmw_fence_obj *fence)
 		container_of(fence, struct vmw_user_fence, fence);
 	struct vmw_fence_manager *fman = fence->fman;
 
-	kfree(ufence);
+	ttm_base_object_kfree(ufence, base);
 	/*
 	 * Free kernel space accounting.
 	 */