SAO PAULO (Reuters) - Republican candidate John McCain may have used his song in the U.S. presidential campaign, but veteran rock 'n' roller Chuck Berry has no doubt whom he wants to see in the White House next year. "America has finally come to this point where you can pick a man of color and that not be a drawback," the legendary 81-year-old guitarist said of Barack Obama, who clinched the Democratic presidential nomination last week and would become the country's first black president if he wins in November. "It's no question, myself being a man of color ... I...