CPU based update doesn't produce a fence, handle such cases properly.
Fixes: d8a3f0a0348d ("drm/amdgpu: implement TLB flush fence")
Signed-off-by: Lang Yu <lang.yu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
 {
        struct amdgpu_vm *vm = params->vm;
 
-       if (!fence || !*fence)
+       tlb_cb->vm = vm;
+       if (!fence || !*fence) {
+               amdgpu_vm_tlb_seq_cb(NULL, &tlb_cb->cb);
                return;
+       }
 
-       tlb_cb->vm = vm;
        if (!dma_fence_add_callback(*fence, &tlb_cb->cb,
                                    amdgpu_vm_tlb_seq_cb)) {
                dma_fence_put(vm->last_tlb_flush);