sch_htb: fix doc warning in htb_add_class_to_row()

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

net/sched/sch_htb.c:351: warning: Function parameter or member 'q' not described in 'htb_add_class_to_row'
net/sched/sch_htb.c:351: warning: Function parameter or member 'cl' not described in 'htb_add_class_to_row'
net/sched/sch_htb.c:351: warning: Function parameter or member 'mask' not described in 'htb_add_class_to_row'
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_htb.c

@@ -349,6 +349,9 @@ static inline void htb_next_rb_node(struct rb_node **n)
 
 /**
  * htb_add_class_to_row - add class to its row
+ * @q: the priority event queue
+ * @cl: the class to add
+ * @mask: the given priorities in class in bitmap
  *
  * The class is added to row at priorities marked in mask.
  * It does nothing if mask == 0.