Fix H7 ADC bug.
Fix H7 ADC bug.

* Fix issue #453
* Use ADC handle to read the used ADC instance.

openmv/openmv,kwagyeman/openmv,iabdalkader/openmv,openmv/openmv,openmv/openmv,kwagyeman/openmv,iabdalkader/openmv,iabdalkader/openmv,kwagyeman/openmv,kwagyeman/openmv,iabdalkader/openmv,openmv/openmv