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.comSigned-off-by: NXiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>