Input: xpad - fix Razer Atrox Arcade Stick button mapping

The "Razer Atrox Arcade Stick" features 10 buttons, and two of them (LT/RT)
don't work properly.  Change its definition in xpad_device[] (mapping
field) to fix.

Signed-off-by: Dario Scarpa <dario.scarpa@duskzone.it>
Signed-off-by: Pavel Rojtberg <rojtberg@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>