RDMA/hns: Don't unregister a callback we didn't register

The driver doesn't actually register an inetaddr notifier function,
so there is no need to unregister it on shutdown.

Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
Signed-off-by: Shaobo Xu <xushaobo2@huawei.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>