A device may have ID_INPUT_JOYSTICK and ID_INPUT_KEY in which case it would
still get added, despite being a joystick device. Make sure we check only the
tablet and joystick bits - where a device has the joystick bit set but not the
tablet one we ignore it.

Note that this check will get removed in the next commit anyway, it's just
here to make tracking the change easier in the history (and figuring out where
potential regressions come from).

Fixes #415



Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>