scsi: qla2xxx: allow session delete to finish before create.

This patch flushes del_work and free_work while sending NACK response for
PRLI

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>