RDMA/hns: Assign the correct value for tx_cqn

When modifying qp from init to init, it need to assign the cqn of send cq
for tx cqn field of qp context. Otherwise, it will cause a mistake when
the send and recv cq sizes are different.

Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>