scsi: qla2xxx: Fix memory corruption during hba reset test

This patch fixes memory corrpution while performing HBA Reset test.

Following stack trace is seen:

[  466.397219] BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
[  466.433669] IP: [<ffffffffc06f5dd0>] qlt_free_session_done+0x260/0x5f0 [qla2xxx]
[  466.467731] PGD 0
[  466.476718] Oops: 0000 [#1] SMP

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>