ASoC: tegra: tegra210_i2s: Fix compile warning with CONFIG_PM=n

Fix trivial compile warnings wrt unused functions by adding
__maybe_unused prefix:
  sound/soc/tegra/tegra210_i2s.c:167:12: warning: 'tegra210_i2s_runtime_suspend' defined but not used [-Wunused-function]
  sound/soc/tegra/tegra210_i2s.c:179:12: warning: 'tegra210_i2s_runtime_resume' defined but not used [-Wunused-function]

Fixes: c0bfa983 ("ASoC: tegra: Add Tegra210 based I2S driver")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200803141850.23713-6-tiwai@suse.deSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/tegra/tegra210_i2s.c

@@ -164,7 +164,7 @@ static int tegra210_i2s_init(struct snd_soc_dapm_widget *w,
 	return tegra210_i2s_sw_reset(compnt, is_playback);
 }
 
-static int tegra210_i2s_runtime_suspend(struct device *dev)
+static int __maybe_unused tegra210_i2s_runtime_suspend(struct device *dev)
 {
 	struct tegra210_i2s *i2s = dev_get_drvdata(dev);
 
@@ -176,7 +176,7 @@ static int tegra210_i2s_runtime_suspend(struct device *dev)
 	return 0;
 }
 
-static int tegra210_i2s_runtime_resume(struct device *dev)
+static int __maybe_unused tegra210_i2s_runtime_resume(struct device *dev)
 {
 	struct tegra210_i2s *i2s = dev_get_drvdata(dev);
 	int err;