ASoC: si476x: Fix IO setup

ASoC: si476x: Fix IO setup

The si476x 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 commit
d6173df35f ("ASoC: si476x: Remove custom register I/O implementation")

Fixes: d6173df35f ("ASoC: si476x: Remove custom register I/O implementation")
Signed-off-by: Lars-Peter Clausen <[email protected]>
Signed-off-by: Mark Brown <[email protected]>
Cc: [email protected]