RDMA/hns: Rename CMDQ head/tail pointer to PI/CI

The same name represents opposite meanings in new/old driver, it is hard
to maintain, so rename them to PI/CI.

Link: https://lore.kernel.org/r/1621482876-35780-2-git-send-email-liweihang@huawei.com


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