staging: iio: light: isl29018: Rename lux_scale to calibscale

This patch renames lux_scale to calibscale and lux_uscale to
ucalibscale.

This is done in order to avoid confusion since these parameters are
used for hardware applied calibration.

Signed-off-by: Roberta Dobrescu <roberta.dobrescu@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>