xfs_bdwrite() cannot return an error; it only queues buffers to the
delayed write list and as such never encounters anything that can fail.
Mark it void.

SGI-PV: 980084
SGI-Modid: xfs-linux-melb:xfs-kern:30825a
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Niv Sardi <xaiki@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>