sch_htb: fix doc warning in htb_lookup_leaf()

Add description for parameters of htb_lookup_leaf()
to fix gcc W=1 warnings:

net/sched/sch_htb.c:773: warning: Function parameter or member 'hprio' not described in 'htb_lookup_leaf'
net/sched/sch_htb.c:773: warning: Function parameter or member 'prio' not described in 'htb_lookup_leaf'
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_htb.c

@@ -799,6 +799,8 @@ static struct rb_node *htb_id_find_next_upper(int prio, struct rb_node *n,
 
 /**
  * htb_lookup_leaf - returns next leaf class in DRR order
+ * @hprio: the current one
+ * @prio: which prio in class
  *
  * Find leaf where current feed pointers points to.
  */