regulator: tps65218.c: fix LS3 issues

- Fix list of valid LS3 currents from mA to µA
- Fix selection of min/max microAmps of LS3.
  Selecting one of the configured values as max value now really
  selects it instead of the next lower one

Signed-off-by: Christian Hohnstaedt <Christian.Hohnstaedt@wago.com>
Signed-off-by: Mark Brown <broonie@kernel.org>