drivers: iio: adc: Modified vbat_sns and bat_id channels

Modified scaling functions for channels Vbat_sns and Bat_Id
to return scaled readings instead of raw code.

Change-Id: I000470ad980516d5387b708d8fa208f222074962
Signed-off-by: Savitri Balagani <savitri@codeaurora.org>
Signed-off-by: Sivasri Kumar Vanka <sivasri@codeaurora.org>