[GFS2] BZ 217008 fsfuzzer fix.

Update the quilt header comments to match the
code changes.

Change gfs2_lookup_simple to return an error in the case
of a NULL inode.
The callers of gfs2_lookup_simple do not check for NULL
in the no entry case and such would end up dereferencing a NULL ptr.

This fixes:
http://projects.info-pull.com/mokb/MOKB-15-11-2006.html



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