[NET]: Fix dev_alloc_skb() typo.

Noticed by Joe Perches.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -279,7 +279,7 @@ struct sk_buff *dev_alloc_skb(unsigned int length)
 {
 	/*
 	 * There is more code here than it seems:
-	 * __def_alloc_skb is an inline
+	 * __dev_alloc_skb is an inline
 	 */
 	return __dev_alloc_skb(length, GFP_ATOMIC);
 }