drivers/net/ftmac100.c: Fix compile warning

Fix this:
ftmac100.c: In function 'ftmac100_initialize':
ftmac100.c:266:12: warning: assignment from incompatible pointer type

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Cc: Joe Hershberger <joe.hershberger@gmail.com>

drivers/net/ftmac100.c

@@ -190,8 +190,7 @@ static int ftmac100_recv (struct eth_device *dev)
 /*
  * Send a data block via Ethernet
  */
-static int
-ftmac100_send (struct eth_device *dev, volatile void *packet, int length)
+static int ftmac100_send(struct eth_device *dev, void *packet, int length)
 {
 	struct ftmac100 *ftmac100 = (struct ftmac100 *)dev->iobase;
 	struct ftmac100_data *priv = dev->priv;