regulator: wm831x: Set the new rather than old value for DVS VSEL

commit 13ae633cf729b0ecb677b75b04886ff8fada8fad upstream.

Reported-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>