scsi: qla2xxx: Fix crash on session cleanup with unload

On unload, session cleanup prematurely gave the signal for driver unload
path to advance.

Link: https://lore.kernel.org/r/20200929102152.32278-6-njavali@marvell.com


Fixes: 726b8548 ("qla2xxx: Add framework for async fabric discovery")
Cc: stable@vger.kernel.org
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Quinn Tran <qutran@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>