RDMA/hns: use page shift of umem instead of constant page shift

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

User application would set page shift of umem, and expect to use
this value during create mr.

Feature or Bugfix: Bugfix

Signed-off-by: Weihang Li <liweihang@hisilicon.com>
Reviewed-by: liuyixian <liuyixian@huawei.com>
Reviewed-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>