ASoC: wm8994: Use pdata cached in MFD driver

This is better style and facilitates implementation of device tree support
for the driver.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

diff --cc sound/soc/codecs/wm8958-dsp2.c
Simple merge

diff --cc sound/soc/codecs/wm8994.c
Simple merge

diff --cc sound/soc/codecs/wm8994.h
Simple merge