ASoC: wm8400: Cleanup manual bias level transitions

Set the CODEC driver's suspend_bias_off flag rather than manually going to
SND_SOC_BIAS_OFF in suspend and SND_SOC_BIAS_STANDBY in resume. This makes
the code a bit shorter and cleaner.

Since the ASoC core now takes care of setting the bias level to
SND_SOC_BIAS_OFF when removing the CODEC there is no need to do it manually
anymore either.

The manual asynchronous transition to SND_SOC_BIAS_STANDBY at the end of
CODEC probe() can also be removed as the core will automatically do this
after the CODEC has been probed. Also running this asynchronously has the
problem of potential race conditions with the core.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>