Input: amijoy - fix Amiga 4-joystick adapter pinout in documentation

Pinout incorrectly duplicated pin 18, correct this.

Signed-off-by: George Anthony Vernon <contact@gvernon.com>
Link: https://lore.kernel.org/r/20250526135957.180254-3-contact@gvernon.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>