iio/adc: ingenic: Fix AUX/VBAT readings when touchscreen is used

iio/adc: ingenic: Fix AUX/VBAT readings when touchscreen is used

When the command feature of the ADC is used, it is possible to program
the ADC, and specify at each step what input should be processed, and in
comparison to what reference.

This broke the AUX and battery readings when the touchscreen was
enabled, most likely because the CMD feature would change the VREF all
the time.

Now, when AUX or battery are read, we temporarily disable the CMD
feature, which means that we won't get touchscreen readings in that time
frame. But it now gives correct values for AUX / battery, and the
touchscreen isn't disabled for long enough to be an actual issue.

Fixes: b96952f498db ("IIO: Ingenic JZ47xx: Add touchscreen mode.")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Artur Rojek <contact@artur-rojek.eu>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20201103201238.161083-1-paul@crapouillou.net
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>