net/sched: fix idr leak in the error path of tcf_act_police_init()

tcf_act_police_init() can fail after the idr has been successfully
reserved (e.g., qdisc_get_rtab() may return NULL). When this happens,
subsequent attempts to configure a police rule using the same idr value
systematiclly fail with -ENOSPC:

 # tc action add action police rate 1000 burst 1000 drop index 100
 RTNETLINK answers: Cannot allocate memory
 We have an error talking to the kernel
 # tc action add action police rate 1000 burst 1000 drop index 100
 RTNETLINK answers: No space left on device
 We have an error talking to the kernel
 # tc action add action police rate 1000 burst 1000 drop index 100
 RTNETLINK answers: No space left on device
 ...

Fix this in the error path of tcf_act_police_init(), calling
tcf_idr_release() in place of tcf_idr_cleanup().

Fixes: 65a206c0 ("net/sched: Change act_api and act_xxx modules to use IDR")
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>