ASoC: wm8904: Fix GPIO and MICBIAS initialisation for regmap conversion

We no longer have a flat ASoC cache so can't peer directly into the array
any more but should instead use the register I/O functions to update the
cache.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: stable@vger.kernel.org (v3.4)