drivers/net: const-ify ethtool_ops declarations

Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
index bf3aa27..4788a41 100644
--- a/drivers/net/gianfar.c
+++ b/drivers/net/gianfar.c
@@ -143,7 +143,7 @@
 static void gfar_clear_exact_match(struct net_device *dev);
 static void gfar_set_mac_for_addr(struct net_device *dev, int num, u8 *addr);
 
-extern struct ethtool_ops gfar_ethtool_ops;
+extern const struct ethtool_ops gfar_ethtool_ops;
 
 MODULE_AUTHOR("Freescale Semiconductor, Inc");
 MODULE_DESCRIPTION("Gianfar Ethernet Driver");