[XFS] Cancel transactions on xfs_itruncate_start error.

SGI-PV: 966502
SGI-Modid: xfs-linux-melb:xfs-kern:28943a

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>