RDMA/hns: avoid potential overflow of

driver inclusion
category: cleanup
bugzilla: NA
CVE: NA

-------------------------------

add brackets to avoid overflow while doing the
calculation.

Reviewed-by: Hu Chunzhi <huchunzhi@huawei.com>
Signed-off-by: Zhao Weibo <zhaoweibo3@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>