RDMA/hns: Remove definition of cq doorbell structure

The struct hns_roce_v2_cq_db is unused, it should be removed.

Link: https://lore.kernel.org/r/1584674622-52773-7-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@mellanox.com>