ASoC: cs4270: Move regulator acquisition to I2C probe()

This is better style since it has us obtaining all resources before we
try the ASoC probe. This change also fixes a potential issue where we
don't enable the regulators before trying to confirm the device ID which
could cause a failure during probe in some system configurations.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Timur Tabi <timur@freescale.com>