scsi: hisi_sas: only process broadcast change in phy_bcast_v2_hw()

There are many BROADCAST primitives generated by the host.
We are only interested in BROADCAST (CHANGE) primitives currently,
so only process this.

Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
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>