By Andrew Holleran Kansas City Chiefs head coach Andy Reid had a 7-word message for his quarterback, Patrick Mahomes, with :13 to play on Sunday night. The Chiefs were trailing the Bills, 36-33, with just :13 remaining on the clock after a touchback kickoff attempt by Buffalo. Kansas City marched down the field and into field goal territory in just a couple of plays, sending the game into overtime when Harrison Butker drilled the game-tying field goal attempt. Reid revealed postgame what he told Mahomes in that moment. “When it’s grim, be the grim reaper,” Reid said. That’s a pretty incredible…