scsi: hisi_sas: Change SERDES_CFG init value to increase reliability of HiLink

With default value of register SERDES_CFG, the link is not stable for some
special disks when running IO. According to HW guys' suggestion, need to
make the bit10~19 value of register SERDES_CFG the max value to increase
the reliability of the HiLink.

Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Reviewed-by: Yupeng Zhou <zhouyupeng1@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>