(Reuters) - Citigroup Inc is shuffling its prime brokerage business, according to an internal memo seen by Reuters, amid reports that the unit could lose millions on a bad loan to an Asian hedge fund.Bloomberg earlier reported that Citi faces a loss of up to $180 million related to risky foreign-exchange bets. Citi and the hedge fund are in talks on how the positions should be valued, the report said. Citi declined to comment on the reported losses.Citi, the third largest U.S. bank by assets,..