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>

Author: g-vernon

Documentation/input/devices/amijoy.rst

@@ -17,7 +17,7 @@ Pin    Meaning  Pin    Meaning
  4     Left1	 8     Left2
  5     Right1	 9     Right2
 13     Fire1	11     Fire2
-18     Gnd1	18     Gnd2
+19     Gnd1	18     Gnd2
 =====  ======== ====   ==========
 
 Amiga digital joystick pinout