[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>

drivers/net/sungem.c

@@ -2896,7 +2896,7 @@ static int __devinit gem_get_device_address(struct gem *gp)
 	if (use_idprom)
 		memcpy(dev->dev_addr, idprom->id_ethaddr, 6);
 #elif defined(CONFIG_PPC_PMAC)
-	unsigned char *addr;
+	const unsigned char *addr;
 
 	addr = get_property(gp->of_node, "local-mac-address", NULL);
 	if (addr == NULL) {