tests: aio: Change reference voltage for AIO

Change reference voltage for Analog comparator to Internal reference
voltage.

Currently AIO is using External reference voltage (Reference A) and
external reference is set at 3.3V. In this usecase both reference
Voltage and AIO IP are set at 3.3V. So rising edge interrupt behaviour
will be unpredictable.

So by changing internal reference voltage to Internal (set at 1.09V)
interrupt will be generated as soon as Voltage on I/P will exceed it.

Jira: ZEP-1927

Signed-off-by: Youvedeep Singh <youvedeep.singh@intel.com>
Signed-off-by: Anas Nashif <anas.nashif@intel.com>