pkt_sched: Fix unlocking in tc_ctl_tfilter()

Fix a bug with spin_lock_bh() inserted instead of spin_unlock_bh() by
some recent patch. 

Reported-by: Denys Fedoryshchenko <denys@visp.net.lb>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>