dm: Remove redundant flush_workqueue() calls

destroy_workqueue() already drains the queue before destroying it, so
there is no need to flush it explicitly.

Remove the redundant flush_workqueue() calls.

This was generated with coccinelle:

@@
expression E;
@@
- 	flush_workqueue(E);
	destroy_workqueue(E);
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-bufio.c

@@ -2082,7 +2082,6 @@ static void __exit dm_bufio_exit(void)
 	int bug = 0;
 
 	cancel_delayed_work_sync(&dm_bufio_cleanup_old_work);
-	flush_workqueue(dm_bufio_wq);
 	destroy_workqueue(dm_bufio_wq);
 
 	if (dm_bufio_client_count) {

drivers/md/dm-zoned-target.c

@@ -967,7 +967,6 @@ static void dmz_dtr(struct dm_target *ti)
 	struct dmz_target *dmz = ti->private;
 	int i;
 
-	flush_workqueue(dmz->chunk_wq);
 	destroy_workqueue(dmz->chunk_wq);
 
 	for (i = 0; i < dmz->nr_ddevs; i++)