By Avi Creditor The 18-year-old U.S. international reportedly has eyes for the Bernabéu and the Bernabéu only. The reigning European champion is coming for the U.S.’s up-and-coming goalkeeping prospect. Real Madrid reportedly had an opening bid for 18-year-old Chicago Fire goalkeeper Gabriel Slonina rejected, with the player’s agent making it clear that Gaga, as he’s casually known, has his sights set on a move to the Bernabéu. Slonina, who recently pledged his international allegiance to the U.S. after being courted by Poland, has become a hot commodity, with Premier League clubs Chelsea and …