[POWERPC] netdevices: Constify & voidify get_property()

Now that get_property() returns a void *, there's no need to cast its
return value. Also, treat the return value as const, so we can
constify get_property later.

powerpc-specific network device driver changes.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/drivers/net/mace.c b/drivers/net/mace.c
index 29e4b5a..5d80e0e 100644
--- a/drivers/net/mace.c
+++ b/drivers/net/mace.c
@@ -113,7 +113,7 @@
 	struct device_node *mace = macio_get_of_node(mdev);
 	struct net_device *dev;
 	struct mace_data *mp;
-	unsigned char *addr;
+	const unsigned char *addr;
 	int j, rev, rc = -EBUSY;
 
 	if (macio_resource_count(mdev) != 3 || macio_irq_count(mdev) != 3) {