s390/qeth: 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.
Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Acked-by: Alexandra Winter <wintera@linux.ibm.com>
Link: https://lore.kernel.org/r/20220216075155.940-1-vulab@iscas.ac.cnSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/s390/net/qeth_l3_main.c

@@ -1961,7 +1961,6 @@ static void qeth_l3_remove_device(struct ccwgroup_device *cgdev)
 	if (card->dev->reg_state == NETREG_REGISTERED)
 		unregister_netdev(card->dev);
 
-	flush_workqueue(card->cmd_wq);
 	destroy_workqueue(card->cmd_wq);
 	qeth_l3_clear_ip_htable(card, 0);
 	qeth_l3_clear_ipato_list(card);