fcoe: add missing destroy_workqueue() on error in fcoe_init()

Add the missing destroy_workqueue() before return from fcoe_init() in
the fcoe transport register failed error handling case.

Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Acked-by: Johannes Thumshirn <jth@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>