Fix system crash due to NULL pointer access.

qlt_plogi_ack_t and fc_port structures were not properly bound before
calling qlt_plogi_ack_unref().

RIP: 0010:qlt_plogi_ack_unref+0xa1/0x150 [qla2xxx]
Call Trace:
qla24xx_create_new_sess+0xb1/0x320 [qla2xxx]
qla2x00_do_work+0x123/0x260 [qla2xxx]
qla2x00_iocb_work_fn+0x30/0x40 [qla2xxx]
process_one_work+0x1f3/0x530
worker_thread+0x4e/0x480
kthread+0x10c/0x140

Fixes: 726b8548 ("qla2xxx: Add framework for async fabric discovery")
Cc: <stable@vger.kernel.org> # 4.10+
Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Giridhar Malavali <giridhar.malavali@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>