ASoC: wm2200: Drop unnecessary dapm bias_level initialization

The default value for the bias_level is SND_SOC_BIAS_OFF when probe is being
called, there is no need to initialize it explicitly.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>