Tyson Foods TSN.N dropped 12.3% on posting a surprise second-quarter loss and cutting its full-year revenue forecast, as prices for its beef and pork declined. By Shreyashi Sanyal and Shristi Achar A May 8 (Reuters) - Wall Street's main indexes were flat on Monday as bleak earnings from companies including Tyson Foods and Catalent clouded a rebound in regional lenders ahead of a key inflation reading this week. On the other end, regional banks' shares stretched gains from a rebound on Friday, with PacWest Bancorp PACW.O jumping 19.9% after the lender sharply cut its quarterly dividend to boost capital.