be2iscsi : Fix kernel panic during reboot/shutdown

 In the reboot/shutdown path, workqueue was destroyed after the
 adapter resource were freed. The task associated with workqueue
 was getting executed after resources were freed. This lead to
 kernel panic.

Signed-off-by: John Soni Jose <sony.john-n@emulex.com>
Signed-off-by: Jayamohan Kallickal <jayamohan.kallickal@emulex.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>