drm/ttm: flush the fence on the bo after we individualize the reservation object

As we move the ttm_bo_individualize_resv() upwards, we need flush the
copied fence too. Otherwise the driver keeps waiting for fence.

run&Kill kfdtest, then perf top.

  25.53%  [ttm]                     [k] ttm_bo_delayed_delete
  24.29%  [kernel]                  [k] dma_resv_test_signaled_rcu
  19.72%  [kernel]                  [k] ww_mutex_lock

Fix: 378e2d5b

("drm/ttm: fix ttm_bo_cleanup_refs_or_queue once more")
Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/series/72339/
Signed-off-by: Christian König <christian.koenig@amd.com>