scsi: hisi_sas: Replace magic number when handle channel interrupt

We use magic number as offset and mask when handle channel interrupt, so
use macro to replace it.

Link: https://lore.kernel.org/r/1579522957-4393-4-git-send-email-john.garry@huawei.com
Signed-off-by: Luo Jiaxing <luojiaxing@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>