config: Handle ganged volume controls better

If the volume control is ganaged stereo instead of
separate left and right controls, use the average the
left and right volumes instead of only using the
left volume value.

Change-Id: Id99b2954ec883fe4c4395b05bfbb83ce52529f71
Signed-off-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
1 file changed