ASoC: rockchip: use __maybe_unused to hide st_irq_syscfg_resume

The rockchip spdif driver uses SIMPLE_DEV_PM_OPS to conditionally
set its power management functions, but we get a warning
about rk_spdif_runtime_resume being unused when CONFIG_PM is not
set:

sound/soc/rockchip/rockchip_spdif.c:67:12: error: 'rk_spdif_runtime_resume' defined but not used [-Werror=unused-function]

This adds a __maybe_unused annotation so the compiler knows
it can silently drop it instead of warning.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/rockchip/rockchip_spdif.c

@@ -54,7 +54,7 @@ static const struct of_device_id rk_spdif_match[] = {
 };
 MODULE_DEVICE_TABLE(of, rk_spdif_match);
 
-static int rk_spdif_runtime_suspend(struct device *dev)
+static int __maybe_unused rk_spdif_runtime_suspend(struct device *dev)
 {
 	struct rk_spdif_dev *spdif = dev_get_drvdata(dev);
 
@@ -64,7 +64,7 @@ static int rk_spdif_runtime_suspend(struct device *dev)
 	return 0;
 }
 
-static int rk_spdif_runtime_resume(struct device *dev)
+static int __maybe_unused rk_spdif_runtime_resume(struct device *dev)
 {
 	struct rk_spdif_dev *spdif = dev_get_drvdata(dev);
 	int ret;