scsi: qla2xxx: Remove unneeded flush_workqueue()

All work currently pending will be done first by calling
destroy_workqueue(). There is no need to flush it explicitly.

Link: https://lore.kernel.org/r/20220424062413.3220315-1-ran.jianping@zte.com.cn


Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ran jianping <ran.jianping@zte.com.cn>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>