drivers/net/xilinx_axi_emac.c: Fix compile warning

Fix this:
xilinx_axi_emac.c: In function 'xilinx_axiemac_initialize':
xilinx_axi_emac.c:646: warning: assignment from incompatible pointer type

Signed-off-by: Stephan Linz <linz@li-pro.net>

drivers/net/xilinx_axi_emac.c

@@ -468,7 +468,7 @@ static int axiemac_init(struct eth_device *dev, bd_t * bis)
 	return 0;
 }
 
-static int axiemac_send(struct eth_device *dev, volatile void *ptr, int len)
+static int axiemac_send(struct eth_device *dev, void *ptr, int len)
 {
 	struct axidma_priv *priv = dev->priv;
 	u32 timeout;