dm-integrity: fix a warning on invalid table line

If we use the 'B' mode and we have an invalit table line,
cancel_delayed_work_sync would trigger a warning. This commit avoids the
warning.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org

Author: Mikulas Patocka

drivers/md/dm-integrity.c

@@ -5164,7 +5164,7 @@ static void dm_integrity_dtr(struct dm_target *ti)
 	BUG_ON(!RB_EMPTY_ROOT(&ic->in_progress));
 	BUG_ON(!list_empty(&ic->wait_list));
 
-	if (ic->mode == 'B')
+	if (ic->mode == 'B' && ic->bitmap_flush_work.work.func)
 		cancel_delayed_work_sync(&ic->bitmap_flush_work);
 	if (ic->metadata_wq)
 		destroy_workqueue(ic->metadata_wq);