ASoC: wcd9xxx: [HACK] Prevent headphone&speaker from clipping

* Buck mode is set to 2V when HPH+Spk combo device has been selected.

Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>

Change-Id: Id9c60be9298cc3eae2fb178900fc95582b00f716