RDMA/hns: Only assign the fields of the rq psn if IB_QP_RQ_PSN is set

Only when the IB_QP_RQ_PSN flags of attr_mask is set is it valid to assign
the relatived fields of rq'psn into the qp context when modified qp.

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