RDMA/hns: fix the bug of out-of-bonds-read in post send

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

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There may be a out-of-bonds-read if qp type is RC in post send.

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