ASoC: pcm512x: Use CONFIG_PM_RUNTIME macro

Fixes the following compilation warnings:
sound/soc/codecs/pcm512x.c:520:12: warning: ‘pcm512x_suspend’ defined but not used [-Wunused-function]
sound/soc/codecs/pcm512x.c:545:12: warning: ‘pcm512x_resume’ defined but not used [-Wunused-function]
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/codecs/pcm512x.c

@@ -517,6 +517,7 @@ void pcm512x_remove(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(pcm512x_remove);
 
+#ifdef CONFIG_PM_RUNTIME
 static int pcm512x_suspend(struct device *dev)
 {
 	struct pcm512x_priv *pcm512x = dev_get_drvdata(dev);
@@ -578,6 +579,7 @@ static int pcm512x_resume(struct device *dev)
 
 	return 0;
 }
+#endif
 
 const struct dev_pm_ops pcm512x_pm_ops = {
 	SET_RUNTIME_PM_OPS(pcm512x_suspend, pcm512x_resume, NULL)