mfd: mc13xxx: Move SPI erratum workaround into SPI I/O function

Move the workaround for double sending AUDIO_CODEC and AUDIO_DAC writes
into the SPI core, aiding refactoring to eliminate the ASoC custom I/O
functions and avoiding the extra writes for I2C.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>