ASoC: tegra: tegra186_dspk: Fix compile warning with CONFIG_PM=n

Fix trivial compile warnings wrt unused functions by adding
__maybe_unused prefix:
  sound/soc/tegra/tegra186_dspk.c:74:12: warning: 'tegra186_dspk_runtime_suspend' defined but not used [-Wunused-function]
  sound/soc/tegra/tegra186_dspk.c:86:12: warning: 'tegra186_dspk_runtime_resume' defined but not used [-Wunused-function]

Fixes: 327ef647 ("ASoC: tegra: Add Tegra186 based DSPK driver")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200803141850.23713-2-tiwai@suse.deSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/tegra/tegra186_dspk.c

@@ -71,7 +71,7 @@ static int tegra186_dspk_put_control(struct snd_kcontrol *kcontrol,
 	return 0;
 }
 
-static int tegra186_dspk_runtime_suspend(struct device *dev)
+static int __maybe_unused tegra186_dspk_runtime_suspend(struct device *dev)
 {
 	struct tegra186_dspk *dspk = dev_get_drvdata(dev);
 
@@ -83,7 +83,7 @@ static int tegra186_dspk_runtime_suspend(struct device *dev)
 	return 0;
 }
 
-static int tegra186_dspk_runtime_resume(struct device *dev)
+static int __maybe_unused tegra186_dspk_runtime_resume(struct device *dev)
 {
 	struct tegra186_dspk *dspk = dev_get_drvdata(dev);
 	int err;