cls_flower: Fix compile error

Fix compile error in net/sched/cls_flower.c

    net/sched/cls_flower.c: In function ‘fl_set_key’:
    net/sched/cls_flower.c:240:3: error: implicit declaration of
     function ‘tcf_change_indev’ [-Werror=implicit-function-declaration]
       err = tcf_change_indev(net, tb[TCA_FLOWER_INDEV]);

Introduced in 77b9900ef5

Fixes: 77b9900ef5 ("tc: introduce Flower classifier")
Signed-off-by: Brian Haley <brian.haley@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_flower.c

@@ -234,15 +234,15 @@ static void fl_set_key_val(struct nlattr **tb,
 static int fl_set_key(struct net *net, struct nlattr **tb,
 		      struct fl_flow_key *key, struct fl_flow_key *mask)
 {
-	int err;
-
+#ifdef CONFIG_NET_CLS_IND
 	if (tb[TCA_FLOWER_INDEV]) {
-		err = tcf_change_indev(net, tb[TCA_FLOWER_INDEV]);
+		int err = tcf_change_indev(net, tb[TCA_FLOWER_INDEV]);
 		if (err < 0)
 			return err;
 		key->indev_ifindex = err;
 		mask->indev_ifindex = 0xffffffff;
 	}
+#endif
 
 	fl_set_key_val(tb, key->eth.dst, TCA_FLOWER_KEY_ETH_DST,
 		       mask->eth.dst, TCA_FLOWER_KEY_ETH_DST_MASK,