net: usb: lan78xx: fix possible skb leak

If skb_linearize() fails, we need to free the skb.

TSO makes skb bigger, and this bug might be the reason
Raspberry Pi 3B+ users had to disable TSO.

Fixes: 55d7de9d ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: RENARD Pierre-Francois <pfrenard@gmail.com>
Cc: Stefan Wahren <stefan.wahren@i2se.com>
Cc: Woojung Huh <woojung.huh@microchip.com>
Cc: Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/lan78xx.c

@@ -2724,11 +2724,6 @@ static int lan78xx_stop(struct net_device *net)
 	return 0;
 }
 
-static int lan78xx_linearize(struct sk_buff *skb)
-{
-	return skb_linearize(skb);
-}
-
 static struct sk_buff *lan78xx_tx_prep(struct lan78xx_net *dev,
 				       struct sk_buff *skb, gfp_t flags)
 {
@@ -2740,8 +2735,10 @@ static struct sk_buff *lan78xx_tx_prep(struct lan78xx_net *dev,
 		return NULL;
 	}
 
-	if (lan78xx_linearize(skb) < 0)
+	if (skb_linearize(skb)) {
+		dev_kfree_skb_any(skb);
 		return NULL;
+	}
 
 	tx_cmd_a = (u32)(skb->len & TX_CMD_A_LEN_MASK_) | TX_CMD_A_FCS_;