A device may disappear and a new device may re-appear with the same device
node while the original device is suspended. Prevent a device resume to open
the wrong device.

In a path context, a changing syspath is the only indicator we get of the
device changing.
In a udev context, if the device was removed and libinput_dispatch() was
called, we can short-cut the syspath comparison by setting it to NULL.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>