ASoC: wsa881x: Set boost voltage level to 6V for WSA8810

Set smart boost voltage level to 6V on WSA8810. This change
will allow audio signal to play on speaker without clipping.

Change-Id: I9b67901d8c1741e82d3ac9653d268132f6c0c06d
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>