ASoC: improve I2C initialization code in CS4270 driver

Further improvements in the I2C initialization sequence of the CS4270 driver.
All ASoC initialization is now done in the I2C probe function.

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