6LoWPAN: use kfree_skb() instead of kfree()

Use kfree_skb() to free sbk_buffs.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ieee802154/6lowpan.c b/net/ieee802154/6lowpan.c
index cf304cc..8a9dbaa 100644
--- a/net/ieee802154/6lowpan.c
+++ b/net/ieee802154/6lowpan.c
@@ -674,7 +674,7 @@
 							sizeof(hdr));
 	return lowpan_skb_deliver(skb, &hdr);
 drop:
-	kfree(skb);
+	kfree_skb(skb);
 	return -EINVAL;
 }