[GFS2] Fix bz 229831, lookup returns wrong inode

The following patch fixes Red Hat bz 229831. Without this patch its
possible for the wrong inode to be returned in certain cases. It is a
pretty unusual event, so that its taken some time to track down. Thanks
and due to Josef Whiter who did a lot of the testing required to thrack
this down and fix it.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>