I don't think we should start from the conclusion of prohibiting AI from voting. We should come up for the criteria for voting and allow anything that meets those criteria vote.

Normally I would say it can be solved by the "shareholder" / "landholder" model. However technically, a sentient AI could own wealth / land. 

Voting rights may need to be restricted to "a corporal shareholder". 

freetx

My view is that all rights are property rights. Voting is privilege, not a right, but we will likely have to refine how one qualifies for that privilege, unless we can abolish the state in the near future.