evdev: when the kernel fuzz is nonzero, set ours to zero

Our udev callout is supposed to reset the kernel fuzz to 0 and move the value
to the LIBINPUT_FUZZ property. This is to stop the kernel from applying its
own hysteresis-like approach.

Where the kernel fuzz is nonzero, something has gone wrong with that approach.
Complain about it and set our fuzz to zero, we are in the hands of the kernel
now. If we leave our fuzz as nonzero, we'll apply our own hysteresis on top of
the kernel's and that leads to unresponsive behavior.

Fixes #313

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