RDMA/hns: Optimize the wr opcode conversion from ib to hns

Simplify the wr opcode conversion from ib to hns by using a map table
instead of the switch-case statement.

Link: https://lore.kernel.org/r/1583839084-31579-4-git-send-email-liweihang@huawei.com
Signed-off-by: Xi Wang <wangxi11@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>