[PATCH] syncppp: incomplete function prototype

This fixes this warning:

  syncppp.c:165: warning: function declaration isn't a prototype

by adding "void" as the function parameter list.

drivers/net/wan/syncppp.c

@@ -161,7 +161,7 @@ static int debug;
  * then put the packet into tx_queue, and call sppp_flush_xmit()
  * after spinlock is released.
  */
-static void sppp_flush_xmit()
+static void sppp_flush_xmit(void)
 {
 	struct sk_buff *skb;
 	while ((skb = skb_dequeue(&tx_queue)) != NULL)