ASoC: sta32x: Fix cache sync

codec->control_data contains a pointer to the regmap struct of the device, not
to the device private data. Use snd_soc_codec_get_drvdata() instead.

The issue was introduced in commit 29fdf4fb ("ASoC: sta32x: Convert to
regmap").

Fixes: 29fdf4fb

 (ASoC: sta32x: Convert to regmap)
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org