Nobody will care. Walker was in his final year or something. 34 credits from graduating, had spent 3 - 4 years at college, been actively there. More to the point, also, 2/3 of the country doesn't have a college degree. Make it an issue, and you are implicitly telling 60% of the voters that they themselves would not be qualified to hold the Presidency.
Walker has probably the equivalent of more than an AA at this point in terms of hours racked up.
It's a non issue. Some people will resent him but the electorate at large isn't educated enough to hold this against him.