RDMA/hns: initialize msg_start_sge_idx field in sq wqe

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

If msg start sge idx in sq wqe is not initialized, data inconsistency
might occur during retransmission.

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>