Input: xpad - remove unused function

There are two definitions of xpad_identify_controller(), one is used
when CONFIG_JOYSTICK_XPAD_LEDS is set, but the other one is empty
and never used, and we get a gcc warning about it:

drivers/input/joystick/xpad.c:1210:13: warning: 'xpad_identify_controller' defined but not used [-Wunused-function]

This removes the second definition.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: cae705ba ("Input: xpad - re-send LED command on present event")
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>