sch_htb: fix doc warning in htb_change_class_mode()

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

net/sched/sch_htb.c:533: warning: Function parameter or member 'q' not described in 'htb_change_class_mode'
net/sched/sch_htb.c:533: warning: Function parameter or member 'cl' not described in 'htb_change_class_mode'
net/sched/sch_htb.c:533: warning: Function parameter or member 'diff' not described in 'htb_change_class_mode'
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_htb.c

@@ -540,6 +540,9 @@ htb_class_mode(struct htb_class *cl, s64 *diff)
 
 /**
  * htb_change_class_mode - changes classe's mode
+ * @q: the priority event queue
+ * @cl: the target class
+ * @diff: diff time in microseconds
  *
  * This should be the only way how to change classe's mode under normal
  * circumstances. Routine will update feed lists linkage, change mode