RDMA/hns: Encapsulate flushing CQE as a function

The process of flushing CQE can be encapsultated into a function, which
can reduce duplicate code.

Link: https://lore.kernel.org/r/1624011020-16992-9-git-send-email-liweihang@huawei.com
Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>