[XFS] A bug was found in xfs_bmap_add_extent_unwritten_real(). In a

particular case, the delta param which is supposed to describe the region
where extents have changed was not updated appropriately.

SGI-PV: 984030

SGI-Modid: xfs-linux-melb:xfs-kern:31663a

Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Olaf Weber <olaf@sgi.com>