ASoC: ak4613: Implement suspend callback

Add the suspend callback to accompany the existing resume operation.
With the suspend/resume callbacks the regmap (regcache) state handling
can follow the recommended sequence.

Based on commit a2ebd586 ("ASoC: ak4642: Implement suspend
callback") by Peter Ujfalusi <peter.ujfalusi@ti.com>.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/ak4613.c

@@ -437,15 +437,25 @@ static struct snd_soc_dai_driver ak4613_dai = {
 	.symmetric_rates = 1,
 };
 
-static int ak4613_resume(struct snd_soc_codec *codec)
+static int ak4613_suspend(struct snd_soc_codec *codec)
 {
 	struct regmap *regmap = dev_get_regmap(codec->dev, NULL);
 
+	regcache_cache_only(regmap, true);
 	regcache_mark_dirty(regmap);
+	return 0;
+}
+
+static int ak4613_resume(struct snd_soc_codec *codec)
+{
+	struct regmap *regmap = dev_get_regmap(codec->dev, NULL);
+
+	regcache_cache_only(regmap, false);
 	return regcache_sync(regmap);
 }
 
 static struct snd_soc_codec_driver soc_codec_dev_ak4613 = {
+	.suspend		= ak4613_suspend,
 	.resume			= ak4613_resume,
 	.set_bias_level		= ak4613_set_bias_level,
 	.controls		= ak4613_snd_controls,