scsi: qla2xxx: Fix mailbox Ch erroneous error

Mailbox Ch/dump ram extend expects mb register 10 to be set. If not
set/clear, firmware can pick up garbage from previous invocation of this
mailbox. Example: mctp dump can set mb10.  On subsequent flash read which
use mailbox cmd Ch, mb10 can retain previous value.

Link: https://lore.kernel.org/r/20210111093134.1206-6-njavali@marvell.com
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>