drm/i915/userptr: Deactivate a failed userptr if the worker reports an EFAULT

drm/i915/userptr: Deactivate a failed userptr if the worker reports an EFAULT

If the worker fails, it no longer has pages to release and can be
immediately removed from the invalidate-tree.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170307205851.32578-1-chris@chris-wilson.co.uk
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>