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/designware.c b/drivers/net/designware.c
index d0d9827..2f923f2 100644
--- a/drivers/net/designware.c
+++ b/drivers/net/designware.c
@@ -451,7 +451,7 @@
 }
 
 #if defined(CONFIG_MII)
-static int dw_mii_read(char *devname, u8 addr, u8 reg, u16 *val)
+static int dw_mii_read(const char *devname, u8 addr, u8 reg, u16 *val)
 {
 	struct eth_device *dev;
 
@@ -462,7 +462,7 @@
 	return 0;
 }
 
-static int dw_mii_write(char *devname, u8 addr, u8 reg, u16 val)
+static int dw_mii_write(const char *devname, u8 addr, u8 reg, u16 val)
 {
 	struct eth_device *dev;