Input: ati_remote2 - switch to using new keycode interface

Switch the code to use new style of getkeycode and setkeycode
methods to allow retrieving and setting keycodes not only by
their scancodes but also by index.

Acked-by: Ville Syrjälä <syrjala@sci.fi>
Tested-by: Jarod Wilson <jarod@wilsonet.com>
Tested-by: Ville Syrjälä <syrjala@sci.fi>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>