scsi: libfc: fix a deadlock in fc_rport_work

In places like fc_rport_recv_plogi_req and fcoe_ctlr_vn_add we always
take the lport disc_mutex lock before the rports mutex
(rp_mutex) lock. Gaurding list_del_rcu(&rdata->peers) with
disc.disc_mutex in fc_rport_work is correct but the rp_mutex lock
can and should to be dropped before taking that lock else results
in a deadlock.

Signed-off-by: Satish Kharat <satishkh@cisco.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>