6lowpan: release device on error path

We recently added a new error path and it needs a dev_put().

Fixes: 7adac1ec8198 ('6lowpan: Only make 6lowpan links to IEEE802154 devices')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ieee802154/6lowpan.c

@@ -1358,8 +1358,10 @@ static int lowpan_newlink(struct net *src_net, struct net_device *dev,
 	real_dev = dev_get_by_index(src_net, nla_get_u32(tb[IFLA_LINK]));
 	if (!real_dev)
 		return -ENODEV;
-	if (real_dev->type != ARPHRD_IEEE802154)
+	if (real_dev->type != ARPHRD_IEEE802154) {
+		dev_put(real_dev);
 		return -EINVAL;
+	}
 
 	lowpan_dev_info(dev)->real_dev = real_dev;
 	lowpan_dev_info(dev)->fragment_tag = 0;