Input: lifebook - don't send incomplete events

When we get a relative packet from trackpoint (when we deal with
touchscreen/trackpoint combo) we should not send events for the device
corresponding to touchscreen as it confuses evtouch driver (it looks
like it keeps previously reported absolute coordinates and the cursor
stays in the same place).

Reported-by: Marcin Drewka <laimoriel@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>