regulator: max8997: Use uV in voltage_map_desc

Current code does integer division (min_vol = min_uV / 1000) before pass
min_vol to max8997_get_voltage_proper_val().
So it is possible min_vol is truncated to a smaller value.

For example, if the request min_uV is 800900 for ldo.
min_vol = 800900 / 1000 = 800 (mV)
Then max8997_get_voltage_proper_val returns 800 mV for this case which is lower
than the requested voltage.

Use uV rather than mV in voltage_map_desc to prevent truncation by integer
division.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: stable@vger.kernel.org