xfs_repair: clear need_root_dotdot if we rebuild the root dir

xfs_repair: clear need_root_dotdot if we rebuild the root dir

It's possible to enter longform_dir2_rebuild with need_root_dotdot
set; rebuilding it will add "..", and if need_root_dotdot stays set,
we'll add another ".." entry, causing a second repair to find and
fix that problem.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>