ieee802154: 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: Stefan Schmidt <stefan@datenfreihafen.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ieee802154/ca8210.c

@@ -2938,9 +2938,7 @@ static int ca8210_dev_com_init(struct ca8210_priv *priv)
  */
 static void ca8210_dev_com_clear(struct ca8210_priv *priv)
 {
-	flush_workqueue(priv->mlme_workqueue);
 	destroy_workqueue(priv->mlme_workqueue);
-	flush_workqueue(priv->irq_workqueue);
 	destroy_workqueue(priv->irq_workqueue);
 }