regulator: wm831x-dcdc: Fix list of wm831x_dcdc_ilim from mA to uA

The wm831x_dcdc_ilim entries needs to be uA because it is used to compare
with min_uA and max_uA.
While at it also make the array const and change to use unsigned int.

Fixes: e4ee831f ("regulator: Add WM831x DC-DC buck convertor support")
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>