xfs: ordered buffer log items are never formatted

xfs: ordered buffer log items are never formatted

BugLink: http://bugs.launchpad.net/bugs/1718412
commit e9385cc6fb7edf23702de33a2dc82965d92d9392 upstream.

Ordered buffers pass through the logging infrastructure without ever
being written to the log. The way this works is that the ordered
buffer status is transferred to the log vector at commit time via
the ->iop_size() callback. In xlog_cil_insert_format_items(),
ordered log vectors bypass ->iop_format() processing altogether.

Therefore it is unnecessary for xfs_buf_item_format() to handle
ordered buffers. Remove the unnecessary logic and assert that an
ordered buffer never reaches this point.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>