power: supply: twl4030_charger: mark OF related data as maybe unused

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

  drivers/power/supply/twl4030_charger.c:1129:34: error: ‘twl_bci_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/twl4030_charger.c

@@ -1126,7 +1126,7 @@ static int twl4030_bci_remove(struct platform_device *pdev)
 	return 0;
 }
 
-static const struct of_device_id twl_bci_of_match[] = {
+static const struct of_device_id twl_bci_of_match[] __maybe_unused = {
 	{.compatible = "ti,twl4030-bci", },
 	{ }
 };