RDMA/hns: Refactor post recv flow

Refactor post recv flow by removing unnecessary checking and removing
duplicated code.

Link: https://lore.kernel.org/r/1611997090-48820-10-git-send-email-liweihang@huawei.com


Signed-off-by: Xi Wang <wangxi11@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>