Brian Steinberg Senior TV EditorSix of the nation’s most prominent advertisers have signed on as early supporters of Univision’s new PrendeTV, a vote of confidence in the streaming service as the Spanish-language broadcaster moves forward in early days under new management.Clorox, Coca-Cola, Dunkin, Johnson & Johnson, Toyota and Walmart will serve as charter advertisers of the new service, Donna Speciale, the executive recently named president of advertising sales and marketing at Univision,