sch_htb: fix doc warning in htb_add_to_id_tree()

Add description for parameters of htb_add_to_id_tree() to fix
gcc W=1 warnings:
net/sched/sch_htb.c:282: warning: Function parameter or member 'root' not described in 'htb_add_to_id_tree'
net/sched/sch_htb.c:282: warning: Function parameter or member 'cl' not described in 'htb_add_to_id_tree'
net/sched/sch_htb.c:282: warning: Function parameter or member 'prio' not described in 'htb_add_to_id_tree'
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_htb.c

@@ -273,6 +273,9 @@ static struct htb_class *htb_classify(struct sk_buff *skb, struct Qdisc *sch,
 
 /**
  * htb_add_to_id_tree - adds class to the round robin list
+ * @root: the root of the tree
+ * @cl: the class to add
+ * @prio: the give prio in class
  *
  * Routine adds class to the list (actually tree) sorted by classid.
  * Make sure that class is not already on such list for given prio.