scsi: qla2xxx: Fix mtcp dump collection failure

MTCP dump failed due to MB Reg 10 was picking garbage data from stack
memory.

Fixes: 81178772 ("[SCSI] qla2xxx: Implemetation of mctp.")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20191217220617.28084-14-hmadhani@marvell.com


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