drivers/net/natsemi.c: Fix compile warning

Fix this:
natsemi.c: In function 'natsemi_initialize':
natsemi.c:338:13: warning: assignment from incompatible pointer type

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

drivers/net/natsemi.c

@@ -237,8 +237,7 @@ static void natsemi_init_txd(struct eth_device *dev);
 static void natsemi_init_rxd(struct eth_device *dev);
 static void natsemi_set_rx_mode(struct eth_device *dev);
 static void natsemi_check_duplex(struct eth_device *dev);
-static int natsemi_send(struct eth_device *dev, volatile void *packet,
-			int length);
+static int natsemi_send(struct eth_device *dev, void *packet, int length);
 static int natsemi_poll(struct eth_device *dev);
 static void natsemi_disable(struct eth_device *dev);
 
@@ -754,8 +753,7 @@ natsemi_check_duplex(struct eth_device *dev)
  * Description: transmits a packet and waits for completion or timeout.
  *
  * Returns:   void.  */
-static int
-natsemi_send(struct eth_device *dev, volatile void *packet, int length)
+static int natsemi_send(struct eth_device *dev, void *packet, int length)
 {
 	u32 i, status = 0;
 	u32 tx_status = 0;