fix attribute error in qos_db
fix attribute error in qos_db

Signed-off-by: huntxu <0e5338760d0f239687243393e6a20f88a8f69100@gmail.com>

huntxu/neutron-qos,huntxu/neutron-qos,eayunstack/neutron-qos,eayunstack/neutron-qos