scsi: csiostor: remove flush_scheduled_work()

flush_scheduled_work() is not required as csio_hw_exit_workers() calls
cancel_work_sync() for hw->evtq_work.

Signed-off-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>