RDMA/hns: Reserve one sge in order to avoid local length error

When rq/srq sge length is smaller than sq sge length, it will produce a
local length error and may cause the bus to hang. Therefore, for rq wqe
and srq wqe, one reserved sge pointing to a reserved mr is used to avoid
this error.

Link: https://lore.kernel.org/r/1588931159-56875-10-git-send-email-liweihang@huawei.com


Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>