RDMA/hns: Simplify the judgment in hns_roce_v2_post_send()

The QP type has been checked in check_send_valid(), if it's not RC, it
will process the UD/GSI branch.

Link: https://lore.kernel.org/r/1624011020-16992-10-git-send-email-liweihang@huawei.com
Signed-off-by: Yixing Liu <liuyixing1@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>