RFC: evdev: don't add devices if grab fails on probe.

[Peter Hutterer]

Currently evdev tries to EVIOCGRAB each input device on probe, but even if the
grab fails the device is added to the server. As a result, each device that is
specified in the xorg.conf is also added by the hotplug code. The hotplugged
device however won't generate any events.

This is confusing for those who want to parse the list of input devices, and I
don't really see the point why we'd want that anyway.
The following patch fixes this by simply failing EvdevProbe if the grab fails.

Comments appreciated, or otherwise I'll stick it into the tree.

Cheers,
  Peter