ASoC: rt5645: add micbias power control select.

We need to set a corresponding control bit before powering micbias up.

Signed-off-by: Bard Liao <bardliao@realtek.com>
[hdegoede@redhat.com: Remove 2 unused variable declarations]
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mark Brown <broonie@kernel.org>