RDMA/hns: fix bug of accessing null pointer

driver inclusion
category: Bugfix
bugzilla: NA
CVE: NA

This modification is mainly to prevent the hem pointer from being emptied
during reset when reset and QP coupling are created, but the QP creation
process is not aware, and access to the null pointer occurs.

Signed-off-by: Tao Jihua <taojihua4@huawei.com>
Reviewed-by: Hu Chunzhi <huchunzhi@huawei.com>
Reviewed-by: Wang Lin <wanglin137@huawei.com>
Reviewed-by: Zhao Weibo <zhaoweibo3@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>