evdev: only extract the fuzz for touchpads and touchscreens

We don't have a hysteresis for tablet devices, so let's leave those as-is.

This may be a slight regression in behavior compared to pre-410b157e now the
kernel will apply the fuzz. Let's see if anyone notices, the fuzz is usually
so tiny on tablets that it shouldn't be noticable.

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