ASoC: wm8903: Move pin configuration into I2C probe() function

Ensure that the device pins are configured as soon as possible by moving
the pin configration (including MICBIAS) into the I2C probe() function.
This had been done in the CODEC probe() function when we were relying on
the ASoC register I/O code.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>