regulator: Add units to limit documentation

The documentation for limits used at protection level setting
did not mention the units. Fix the units in documentation to
match values passed in from device-tree (uV, uA, Kelvin) to
avoid confusion.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Link: https://lore.kernel.org/r/111114aca991e41e49a32f89b74e95285f07c1e3.1637233864.git.matti.vaittinen@fi.rohmeurope.com


Signed-off-by: Mark Brown <broonie@kernel.org>