I have hunted squirrels for 48 years an have never seen white spots on the liver. I killed a fox squirrel couple years back that had a bad case of mange, only one I killed that was sick.
I would say you are probably OK to eat them as long as the meat is well cooked. You might want to check with your local game department to see if there is a disease problem with the squirrels in your state. As long as they appeared healthy an didn't act sick, I don't see a problem, myself.