ASoC: 88pm860: Fix IO setup

The 88pm860 is a MFD device and the CODEC driver is using the regmap struct of
the parent device, hence automatic IO setup will not work and we need to
manually call snd_soc_codec_set_cache_io(). The issue was introduced in commit
f9ded3b2 ("ASoC: 88pm860x: Use regmap for I/O").

Fixes: f9ded3b2

 ("ASoC: 88pm860x: Use regmap for I/O").
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org