wireless: Remove redundant 'flush_workqueue()' calls

[ Upstream commit ff1cc2fa ]

'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: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/0855d51423578ad019c0264dad3fe47a2e8af9c7.1633849511.git.christophe.jaillet@wanadoo.fr


Stable-dep-of: cb5942b7 ("wifi: wilc1000: prevent use-after-free on vif when cleaning up all interfaces")
Signed-off-by: Sasha Levin <sashal@kernel.org>