ASoC: tegra: tegra210_ahub: Fix compile warning with CONFIG_PM=n

Fix trivial compile warnings wrt unused functions by adding
__maybe_unused prefix:
  sound/soc/tegra/tegra210_ahub.c:567:12: warning: 'tegra_ahub_runtime_suspend' defined but not used [-Wunused-function]
  sound/soc/tegra/tegra210_ahub.c:579:12: warning: 'tegra_ahub_runtime_resume' defined but not used [-Wunused-function]

Fixes: 16e1bcc2 ("ASoC: tegra: Add Tegra210 based AHUB driver")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200803141850.23713-4-tiwai@suse.deSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/tegra/tegra210_ahub.c

@@ -564,7 +564,7 @@ static const struct of_device_id tegra_ahub_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, tegra_ahub_of_match);
 
-static int tegra_ahub_runtime_suspend(struct device *dev)
+static int __maybe_unused tegra_ahub_runtime_suspend(struct device *dev)
 {
 	struct tegra_ahub *ahub = dev_get_drvdata(dev);
 
@@ -576,7 +576,7 @@ static int tegra_ahub_runtime_suspend(struct device *dev)
 	return 0;
 }
 
-static int tegra_ahub_runtime_resume(struct device *dev)
+static int __maybe_unused tegra_ahub_runtime_resume(struct device *dev)
 {
 	struct tegra_ahub *ahub = dev_get_drvdata(dev);
 	int err;