regulator: wm831x-dcdc: Ensure selected voltage falls within requested range

Use DIV_ROUND_UP to ensure selected voltage won't less than min_uV due to
integer truncation.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
1 file changed