Input: wacom_w8001 - handle touch error case correctly

If a device failed at the pen setup and gets a zero reply from the touch
device, we need to return an error. Otherwise we have a device with
nothing but a name and the EV_KEY and EV_ABS bits.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>