irqchip/meson-gpio: Mark OF related data as maybe unused

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

  drivers/irqchip/irq-meson-gpio.c:153:34: error: ‘meson_irq_gpio_matches’ defined but not used [-Werror=unused-const-variable=]
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230512164506.212267-1-krzysztof.kozlowski@linaro.org

drivers/irqchip/irq-meson-gpio.c

@@ -150,7 +150,7 @@ static const struct meson_gpio_irq_params s4_params = {
 	INIT_MESON_S4_COMMON_DATA(82)
 };
 
-static const struct of_device_id meson_irq_gpio_matches[] = {
+static const struct of_device_id meson_irq_gpio_matches[] __maybe_unused = {
 	{ .compatible = "amlogic,meson8-gpio-intc", .data = &meson8_params },
 	{ .compatible = "amlogic,meson8b-gpio-intc", .data = &meson8b_params },
 	{ .compatible = "amlogic,meson-gxbb-gpio-intc", .data = &gxbb_params },