Singer-songwriter Bruno Mars used to make a living playing professional poker. Not anymore, apparently. According to NewsNation, Mars, who was born Peter Gene Hernandez in 1985, has racked up a gambling debt with MGM in the tens of millions of dollars. “He owes millions to the MGM (from gambling),” a source the outlet described as a “well placed Vegas insider” said. “They basically own him.” In fact, the source said, Mars’s gambling has put him in debt to the casino to the tune of $50 million. Of course, $50 million isn’t to Mars what it might be for the average American, given his income brac…