hisi_sas: use device linkrate in MCR for v2 hw

Contrary to the field name, the MCR (max connection rate) in the ITCT
should hold the device linkrate (linkrate of the connected phy), and not
the max linkrate.

This fixes an issue seen where some SATA drives connected through an
expander which would not attach.

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>