By Janina Nuno Rios and Angelica Medina MEXICO CITY, June 10 (Reuters) - FIFA President Gianni Infantino defended the way soccer's governing body had handled visa issues ahead of the World Cup, saying on Wednesday that it was working to find solutions but could not override government decisions. Speaking on the eve of the tournament opener between co-hosts Mexico and South Africa, Infantino addressed concerns surrounding Somali referee Omar Abdulkadir Artan, who was barred from entering the U.S. despite having a valid visa.