net: change the env name to use const

As we don't modify the 'name' parameter, so change it to const.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/include/net.h b/include/net.h
index 3a787cc..1aabd74 100644
--- a/include/net.h
+++ b/include/net.h
@@ -233,8 +233,8 @@
 
 int eth_get_dev_index(void);		/* get the device index */
 void eth_parse_enetaddr(const char *addr, uchar *enetaddr);
-int eth_getenv_enetaddr(char *name, uchar *enetaddr);
-int eth_setenv_enetaddr(char *name, const uchar *enetaddr);
+int eth_getenv_enetaddr(const char *name, uchar *enetaddr);
+int eth_setenv_enetaddr(const char *name, const uchar *enetaddr);
 
 /*
  * Get the hardware address for an ethernet interface .
diff --git a/net/eth.c b/net/eth.c
index e9b22d8..b978aae 100644
--- a/net/eth.c
+++ b/net/eth.c
@@ -31,13 +31,13 @@
 	}
 }
 
-int eth_getenv_enetaddr(char *name, uchar *enetaddr)
+int eth_getenv_enetaddr(const char *name, uchar *enetaddr)
 {
 	eth_parse_enetaddr(getenv(name), enetaddr);
 	return is_valid_ethaddr(enetaddr);
 }
 
-int eth_setenv_enetaddr(char *name, const uchar *enetaddr)
+int eth_setenv_enetaddr(const char *name, const uchar *enetaddr)
 {
 	char buf[20];