[XFS] Fix uninitialized br_state and br_startoff in

xfs_bmap_add_extent_delay_real()

SGI-PV: 957008
SGI-Modid: xfs-linux-melb:xfs-kern:27457a

Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Shailendra Tripathi <stripathi@agami.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>