power: supply: ltc4162-l-charger: mark OF related data as maybe unused

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

  drivers/power/supply/ltc4162-l-charger.c:911:34: error: ‘ltc4162l_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/ltc4162-l-charger.c

@@ -908,7 +908,7 @@ static const struct i2c_device_id ltc4162l_i2c_id_table[] = {
 };
 MODULE_DEVICE_TABLE(i2c, ltc4162l_i2c_id_table);
 
-static const struct of_device_id ltc4162l_of_match[] = {
+static const struct of_device_id ltc4162l_of_match[] __maybe_unused = {
 	{ .compatible = "lltc,ltc4162-l", },
 	{ },
 };