Late Late Show's Carpool Karaoke snagged Paul McCartney for this year’s London visit. It’s not so much karaoke and, technically, not so much “carpool” either with lots of trips down Beatles Liverpool Memory Lane, or Penny Lane to be more precise. Beginning their Liverpool "road trip" to “Baby You Can Drive My Car,” of course, host James Corden asks the former Beatle how old he was when he wrote his first song. He was 14 and it was called “I Lost My Little Girl”: I woke up…