power: supply: rt9455_charger: mark OF related data as maybe unused

The driver can be compile tested with !CONFIG_OF making certain data
unused:

  drivers/power/supply/rt9455_charger.c:1725:34: error: ‘rt9455_of_match’ defined but not used [-Werror=unused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/rt9455_charger.c

@@ -1722,7 +1722,7 @@ static const struct i2c_device_id rt9455_i2c_id_table[] = {
 };
 MODULE_DEVICE_TABLE(i2c, rt9455_i2c_id_table);
 
-static const struct of_device_id rt9455_of_match[] = {
+static const struct of_device_id rt9455_of_match[] __maybe_unused = {
 	{ .compatible = "richtek,rt9455", },
 	{ },
 };