By Matt Cronin CARLSBAD, California (Reuters) – Switzerland's former world number one Martina Hingis said her renewed hunger for competition inspired her forthcoming comeback in doubles but she has no plans to return in singles. Hingis is teaming up with Slovak Daniela Hantuchova at this week's Southern California Open with the pair slated to play an evening match on Wednesday against Julia Goerges of Germany and Darija Jurak of Croatia. Hingis, who was inducted into the International Tennis Hall of fame just two weeks ago, has not played a WTA-level match since 2007. …