scsi: hisi_sas: Tidy hisi_sas_task_prep()

scsi: hisi_sas: Tidy hisi_sas_task_prep()

BugLink: https://bugs.launchpad.net/bugs/1794165
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>
(cherry picked from commit 6cca51ee0aa2540d648ff8698c3889330d897f27)
Signed-off-by: dann frazier <dann.frazier@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>