ASoC: ab8500-codec: Revert back to regmap

ASoC: ab8500-codec: Revert back to regmap

Commit 66cddb0d701d ("ASoC: ab8500: Convert register I/O to regmap")
initially converted the ab8500 CODEC driver to use regmap rather than
legacy ASoC IO. This was reverted though in commit e243e93ecc79 ("ASoC:
ab8500: Revert to using custom I/O functions") since the inital conversion
was not working properly. This was presumebly because the SOC_SINGLE_XR_SX
controls, which are used by this driver, did not properly support regmap at
that point. This has since been fixed in commit d112ca967034 ("ASoC: Prepare
SOC_SINGLE_XR_SX controls for regmap"). So revert back to regmap again.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>