RDMA/hns: Simplify the qp state convert code

Use type map table to reduce the cyclomatic complexity.

Link: https://lore.kernel.org/r/1586938475-37049-4-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>