scsi: hisi_sas: Set the BIST init value before enabling BIST

If set the BIST init value after enabling BIST, there may be still some few
error bits. According to the process, need to set the BIST init value
before enabling BIST.

Fixes: 97b151e7 ("scsi: hisi_sas: Add BIST support for phy loopback")
Link: https://lore.kernel.org/r/1571926105-74636-3-git-send-email-john.garry@huawei.com


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>