RDMA/hns: Remove magic number

Don't use unintelligible constants.

Link: https://lore.kernel.org/r/20211119140208.40416-10-liangwenpeng@huawei.com


Signed-off-by: Xinhao Liu <liuxinhao5@hisilicon.com>
Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>