ASoC: wm8903: Move interrupt request to I2C probe

There's no reason to defer requesting of the interrupt until the CODEC
probe and doing so results in more work if we hit an error as we'll have
registered the CODEC with the core. It's neater to acquire as many of the
resources we'll need as we can in the bus probe function.

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