ASoC: wcd937x: Change vbg fine voltage to 0.5V for wcd937x second source

VBG Fine Voltage should be changed to 0.5V for second source
target. Set it to corresponding value in init.

Change-Id: Ica73f45d7cb4f5f623d3333680894625603ca92c
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>