iio: adc: qcom-vadc-common: Change ADC7 die_temp output unit to mC

Change ADC7 die_temp output unit from C to mC, as thermal
framework expects temperatures to be reported in mC.

Change-Id: Ie14b745f7db625f399ac5f79b3467a1654ea4a21
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>