RDMA/hns: Use new interface to write DB related fields

Use hr_write_reg() instead of roce_set_field().

Link: https://lore.kernel.org/r/1624262443-24528-9-git-send-email-liweihang@huawei.com
Signed-off-by: Yixing Liu <liuyixing1@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>