RDMA/hns: Refactor process of posting CMDQ

Simplify __hns_roce_cmq_send() then remove the redundant variables.

Link: https://lore.kernel.org/r/1612688143-28226-6-git-send-email-liweihang@huawei.com


Signed-off-by: Lang Cheng <chenglang@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>