power: supply: make device_attribute const

Make these const as they are only passed as an argument to the
function device_create_file and device_remove_file and the corresponding
arguments are of type const.
Done using Coccinelle.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>

drivers/power/supply/olpc_battery.c

@@ -559,7 +559,7 @@ static ssize_t olpc_bat_error_read(struct device *dev,
 	return sprintf(buf, "%d\n", ec_byte);
 }
 
-static struct device_attribute olpc_bat_error = {
+static const struct device_attribute olpc_bat_error = {
 	.attr = {
 		.name = "error",
 		.mode = S_IRUGO,