scsi: qla2xxx: Fix partial flash write of MBI

For new adapters with multiple flash regions to write to, current code
allows FW & Boot regions to be written, while other regions are blocked via
sysfs. The fix is to block all flash read/write through sysfs interface.

Fixes: e81d1bcb

 ("scsi: qla2xxx: Further limit FLASH region write access from SysFS")
Cc: stable@vger.kernel.org # 5.2
Link: https://lore.kernel.org/r/20191022193643.7076-3-hmadhani@marvell.com
Signed-off-by: Quinn Tran <qutran@marvell.com>
Signed-off-by: Girish Basrur <gbasrur@marvell.com>
Signed-off-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>