RDMA/hns: Fix non-standard error codes

It is better to return a linux error code than define a private constant.

Link: https://lore.kernel.org/r/1572952082-6681-9-git-send-email-liweihang@hisilicon.com


Signed-off-by: Yixian Liu <liuyixian@huawei.com>
Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Weihang Li <liweihang@hisilicon.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>