This does not cause any conflict with CAN-bus. But keep in mind than any such adapter always draw a bit of current as long as it stays connected, even if not used by a USB device. Unless you drive daily, this will eventually drain your battery.
Going the route as described by previous posts will be a better solution.
If you insists on a permanent connection, make sure to connect it via a relay that will switch it of when not driving the bike.
If you intend to charge phone/helmet at a coffee brake, I would suggest to pick up a rechargeable battery-bank.