ASoC: wm8903: Move register default changes to I2C probe

Also convert to use update_bits() while we're at it. No great need to do
this, it's just a bit neater to do as much as possible in the I2C probe.

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