(Bloomberg) -- Mubadala Capital is exploring an acquisition of Clear Channel Outdoor Holdings Inc., according to people familiar with the matter.The asset management arm of Abu Dhabi sovereign wealth fund Mubadala Investment Co. has been working on a potential deal for the billboard operator, the people said, asking not to be identified because the matter is private.Clear Channel Outdoor shares rose 9.5% Friday, giving the company a market value of $773 million. The company has about$6.4 billion in debt, a ...