vrf: fix NULL dereference in vrf_finish_output()

The "skb" pointer is NULL on this error path so we can't dereference it.
Use "dev" instead.

Fixes: 14ee70ca ("vrf: use skb_expand_head in vrf_finish_output")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20210806150435.GB15586@kiliSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/vrf.c

@@ -864,7 +864,7 @@ static int vrf_finish_output(struct net *net, struct sock *sk, struct sk_buff *s
 	if (unlikely(skb_headroom(skb) < hh_len && dev->header_ops)) {
 		skb = skb_expand_head(skb, hh_len);
 		if (!skb) {
-			skb->dev->stats.tx_errors++;
+			dev->stats.tx_errors++;
 			return -ENOMEM;
 		}
 	}