RDMA/hns: Remove redundant member doorbell_qpn of struct hns_roce_qp

The value of doorbell_qpn is always equal to qpn on current hardware
versions. So remove it.

Link: https://lore.kernel.org/r/20220829105021.1427804-5-liangwenpeng@huawei.com


Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>