net: sched: fix block->refcnt decrement

Currently the refcnt is never decremented in case the value is not 1.
Fix it by adding decrement in case the refcnt is not 1.

Reported-by: Vlad Buslov <vladbu@mellanox.com>
Fixes: f71e0ca4db18 ("net: sched: Avoid implicit chain 0 creation")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_api.c

@@ -780,6 +780,8 @@ void tcf_block_put_ext(struct tcf_block *block, struct Qdisc *q,
 		block->refcnt--;
 		if (list_empty(&block->chain_list))
 			kfree(block);
+	} else {
+		block->refcnt--;
 	}
 }
 EXPORT_SYMBOL(tcf_block_put_ext);