drm/amd/amdgpu:flush ttm delayed work before cancel_sync

[Why]
In some cases when we unload driver, warning call trace
will show up in vram_mgr_fini which claims that LRU is not empty, caused
by the ttm bo inside delay deleted queue.

[How]
We should flush delayed work to make sure the delay deleting is done.
Signed-off-by: YuBiao Wang <YuBiao.Wang@amd.com>
Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -3826,8 +3826,10 @@ void amdgpu_device_fini_hw(struct amdgpu_device *adev)
 {
 	dev_info(adev->dev, "amdgpu: finishing device.\n");
 	flush_delayed_work(&adev->delayed_init_work);
-	if (adev->mman.initialized)
+	if (adev->mman.initialized) {
+		flush_delayed_work(&adev->mman.bdev.wq);
 		ttm_bo_lock_delayed_workqueue(&adev->mman.bdev);
+	}
 	adev->shutdown = true;
 
 	/* make sure IB test finished before entering exclusive mode