(Reuters) – When Eloy Perez fights holder Adrien Broner for the WBO super featherweight title next month in St. Louis, he will have in his corner an inspirational nine-year-old boy whom he regards as the ultimate warrior. Sy Sherman, the boxer's official belt carrier, was diagnosed with primary liver cancer 11 months ago but he has been a source of optimism ever since he joined the Perez team …