tty: serial: max3100: 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>
Link: https://lore.kernel.org/r/20220114085156.43041-1-vulab@iscas.ac.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/max3100.c

@@ -554,7 +554,6 @@ static void max3100_shutdown(struct uart_port *port)
 		del_timer_sync(&s->timer);
 
 	if (s->workqueue) {
-		flush_workqueue(s->workqueue);
 		destroy_workqueue(s->workqueue);
 		s->workqueue = NULL;
 	}