drivers/net/dm9000x.c: Fix compile warning

Fix this:
dm9000x.c: In function 'dm9000_initialize':
dm9000x.c:636:12: warning: assignment from incompatible pointer type

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

drivers/net/dm9000x.c

@@ -406,8 +406,7 @@ static int dm9000_init(struct eth_device *dev, bd_t *bd)
   Hardware start transmission.
   Send a packet to media from the upper layer.
 */
-static int dm9000_send(struct eth_device *netdev, volatile void *packet,
-		     int length)
+static int dm9000_send(struct eth_device *netdev, void *packet, int length)
 {
 	int tmo;
 	struct board_info *db = &dm9000_info;