RDMA/hns: Simplify the cqe code of poll cq

Encapsulate codes to get status of cqe into a function and use map table
instead of switch-case to reduce cyclomatic complexity of
hns_roce_v2_poll_one().

Link: https://lore.kernel.org/r/1586938475-37049-5-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>