Fix compile warnings for const correctness

Commit 6e37b1a3a25004d3df5867de49fff6b3fc9c4f04 modifies several net calls
to take a (const char *) parameter instead of (char *), but in some cases
the modified functions call other functions taking (char *).  The end result
is warnings about discarding the const qualifier.

This patch fixes these other function signatures.

Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
diff --git a/drivers/net/phy/miiphybb.c b/drivers/net/phy/miiphybb.c
index 2768c75..1045cf1 100644
--- a/drivers/net/phy/miiphybb.c
+++ b/drivers/net/phy/miiphybb.c
@@ -143,7 +143,7 @@
 	}
 }
 
-static inline struct bb_miiphy_bus *bb_miiphy_getbus(char *devname)
+static inline struct bb_miiphy_bus *bb_miiphy_getbus(const char *devname)
 {
 #ifdef CONFIG_BITBANGMII_MULTI
 	int i;
@@ -246,7 +246,7 @@
  * Returns:
  *   0 on success
  */
-int bb_miiphy_read(char *devname, unsigned char addr,
+int bb_miiphy_read(const char *devname, unsigned char addr,
 		   unsigned char reg, unsigned short *value)
 {
 	short rdreg; /* register working value */
@@ -327,7 +327,7 @@
  * Returns:
  *   0 on success
  */
-int bb_miiphy_write (char *devname, unsigned char addr,
+int bb_miiphy_write (const char *devname, unsigned char addr,
 		     unsigned char reg, unsigned short value)
 {
 	struct bb_miiphy_bus *bus;