net/sched: cbs: Fix error path of cbs_module_init

If register_qdisc fails, we should unregister
netdevice notifier.

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: e0a7683d ("net/sched: cbs: fix port_rate miscalculation")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>