scsi: fnic: Remove redundant flush_workqueue() calls

scsi: fnic: 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.

This was generated with coccinelle:

@@
expression E;
@@
- flush_workqueue(E);
  destroy_workqueue(E);

Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Link: https://lore.kernel.org/r/20250312074320.1430175-1-nichen@iscas.ac.cn
Reviewed-by: Karan Tilak Kumar <kartilak@cisco.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>