V4L/DVB (9266): videobuf: properly handle attachment failure

This fixes attachment failure where we now unwind
attachment and skip non-attached nodes where
necessary so we can survive a fault situation
correctly.

Signed-off-by: Darron Broad <darron@kewl.org>
Signed-off-by: Steven Toth <stoth@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>