(Reuters) – Warren Buffett said Berkshire Hathaway Inc’s recent investment in Activision Blizzard Inc has been “no bonanza” for Berkshire, and was made without knowing the video game maker would receive a takeover offer from Microsoft Corp. In a letter released by Buffett’s office on Thursday, Buffett said one of his investment managers paid about $77 per share for Berkshire’s 14.7 million Activision shares, acquiring about 85% of his position in October and the rest in November. Buffett also said Berkshire had “no prior knowledge” that Microsoft was working on a $68.7 billion takeover of Acti…