iio: rradc: Remove scaled support for battery thermistor

The battery thermistor values are not scaled to the
appropriate units from the ADC code on the round robin
ADC (RRADC) channel data registers. Remove support to
read the scaled results for this channel and expose
only reading the raw ADC code.

Change-Id: I6ff45d25f18063cbed70181b22ab0b07b4da4dc1
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>