To decrease the usage of spinlock during delivery IO, relocate some code in
hisi_sas_task_prep().

Also an invalid comment is removed.
Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>