By Jonathan Stempel OMAHA, Neb. (Reuters) -Warren Buffett said on Saturday that Berkshire Hathaway Inc has taken a 9.5% stake in Activision Blizzard Inc, and built most of that stake after Microsoft Corp agreed to buy the video game maker for $68.7 billion. Buffett disclosed the investment at Berkshire’s annual shareholder meeting in Omaha, Nebraska. The investment is a wager that Microsoft may complete its proposed $95-per-share takeover of Activision, whose franchises include “Call of Duty” and “Candy Crush,” and overcome expected tough antitrust scrutiny from the U.S. Department of Justice….