miiphy: constify device name

The driver name does not need to be writable, so constify it.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
diff --git a/drivers/net/4xx_enet.c b/drivers/net/4xx_enet.c
index 144b851..d9487ad 100644
--- a/drivers/net/4xx_enet.c
+++ b/drivers/net/4xx_enet.c
@@ -305,9 +305,9 @@
 static void emac_err (struct eth_device *dev, unsigned long isr);
 
 extern int phy_setup_aneg (char *devname, unsigned char addr);
-extern int emac4xx_miiphy_read (char *devname, unsigned char addr,
+extern int emac4xx_miiphy_read (const char *devname, unsigned char addr,
 		unsigned char reg, unsigned short *value);
-extern int emac4xx_miiphy_write (char *devname, unsigned char addr,
+extern int emac4xx_miiphy_write (const char *devname, unsigned char addr,
 		unsigned char reg, unsigned short value);
 
 int board_emac_count(void);