drivers/net/usb/usbnet.c: Use FIELD_SIZEOF macro in usbnet_init() function.

Signed-off-by: NThiago Farina <tfransosi@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/usbnet.c

@@ -1529,9 +1529,9 @@ EXPORT_SYMBOL_GPL(usbnet_resume);
 
 static int __init usbnet_init(void)
 {
-	/* compiler should optimize this out */
-	BUILD_BUG_ON (sizeof (((struct sk_buff *)0)->cb)
-			< sizeof (struct skb_data));
+	/* Compiler should optimize this out. */
+	BUILD_BUG_ON(
+		FIELD_SIZEOF(struct sk_buff, cb) < sizeof(struct skb_data));
 
 	random_ether_addr(node_id);
 	return 0;