scsi: hisi_sas: keep CHL_INT2 masked for v2 HW

None of the CHL_INT2 interrupts are serviced in the channel irq ISR, so
leave the interrupt source masked.  The interrupt mask is initially set
in init_reg_v2_hw().

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>