They almost certainly aren't USB chargers. Probably USB ports for inserting thumb drives to update the navigational charts. These kinds of USB ports are [mis]used for charging phones all the time, and the phone can end up being mounted as a mass-storage device.
No idea how the rest of the exploit would work in this scenario though, I have a hard time believing it.
If the USB chargers in cockpits are any more complex than the above, why?