Input: ati_remote - add missing input_sync()

When emulating button toggle drivers need to send input_sync()
between 'down' and 'up' events, otherwise some users might miss
keypress because device's state is only considered finalized
after EV_SYN/SYN_REPORT is received.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>