iio: adc: qcom-vadc-common: simplify qcom_vadc_map_voltage_temp

All volt-temp tables here are sorted in descending order. There is no
need to accout for (unused) ascending table sorting case, so simplify
the conversion function.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20201204025509.1075506-11-dmitry.baryshkov@linaro.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>