ASoC: sgtl5000: Fix suspend/resume

Commit 8419caa7 ("ASoC: sgtl5000: Do not disable regulators in
SND_SOC_BIAS_OFF") causes the sgtl5000 to fail after a suspend/resume
sequence:

Playing WAVE '/media/a2002011001-e02.wav' : Signed 16 bit Little
Endian, Rate 44100 Hz, Stereo
aplay: pcm_write:2051: write error: Input/output error

The problem is caused by the fact that the aforementioned commit
dropped the cache handling, so re-introduce the register map
resync to fix the problem.
Suggested-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: <stable@vger.kernel.org>

sound/soc/codecs/sgtl5000.c

@@ -876,15 +876,26 @@ static int sgtl5000_pcm_hw_params(struct snd_pcm_substream *substream,
 static int sgtl5000_set_bias_level(struct snd_soc_codec *codec,
 				   enum snd_soc_bias_level level)
 {
+	struct sgtl5000_priv *sgtl = snd_soc_codec_get_drvdata(codec);
+	int ret;
+
 	switch (level) {
 	case SND_SOC_BIAS_ON:
 	case SND_SOC_BIAS_PREPARE:
 	case SND_SOC_BIAS_STANDBY:
+		regcache_cache_only(sgtl->regmap, false);
+		ret = regcache_sync(sgtl->regmap);
+		if (ret) {
+			regcache_cache_only(sgtl->regmap, true);
+			return ret;
+		}
+
 		snd_soc_update_bits(codec, SGTL5000_CHIP_ANA_POWER,
 				    SGTL5000_REFTOP_POWERUP,
 				    SGTL5000_REFTOP_POWERUP);
 		break;
 	case SND_SOC_BIAS_OFF:
+		regcache_cache_only(sgtl->regmap, true);
 		snd_soc_update_bits(codec, SGTL5000_CHIP_ANA_POWER,
 				    SGTL5000_REFTOP_POWERUP, 0);
 		break;