Input: xpad - demote non-conformant kernel-doc header

Input: xpad - demote non-conformant kernel-doc header

Fixes the following W=1 kernel build warning(s):

 drivers/input/joystick/xpad.c:1361: warning: Function parameter or member 'xpad' not described in 'xpad_send_led_command'
 drivers/input/joystick/xpad.c:1361: warning: Function parameter or member 'command' not described in 'xpad_send_led_command'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201112110204.2083435-2-lee.jones@linaro.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>