ASoC: wm8994: Remove the set_cache_io() entirely from ASoC probe.

As we can set the CODEC I/O while snd_soc_register_codec(), so the
calling of set_cache_io() from CODEC ASoC probe could be removed
entirely.

And then we can set the CODEC I/O in the device probe instead of
CODEC ASoC probe as earily as possible.

Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>