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/macb.c b/drivers/net/macb.c
index 6a58a37..acb8d20 100644
--- a/drivers/net/macb.c
+++ b/drivers/net/macb.c
@@ -167,7 +167,7 @@
 
 #if defined(CONFIG_CMD_MII)
 
-int macb_miiphy_read(char *devname, u8 phy_adr, u8 reg, u16 *value)
+int macb_miiphy_read(const char *devname, u8 phy_adr, u8 reg, u16 *value)
 {
 	struct eth_device *dev = eth_get_dev_by_name(devname);
 	struct macb_device *macb = to_macb(dev);
@@ -180,7 +180,7 @@
 	return 0;
 }
 
-int macb_miiphy_write(char *devname, u8 phy_adr, u8 reg, u16 value)
+int macb_miiphy_write(const char *devname, u8 phy_adr, u8 reg, u16 value)
 {
 	struct eth_device *dev = eth_get_dev_by_name(devname);
 	struct macb_device *macb = to_macb(dev);