scsi: iscsi: Change iSCSI workqueue max_active back to 1

Commit 3ce41966

 ("scsi: iscsi: Register sysfs for iscsi workqueue")
enabled 'cpumask' support for iSCSI workqueues. However, it is unnecessary
to set max_active = 2 since 'cpumask' can still be modified when max_active
is 1.

This patch sets max_active to 1 so as to keep the same behaviour as before.

Link: https://lore.kernel.org/r/20200701030745.16897-1-bob.liu@oracle.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>