Per Dave Chinner suggestion, this patch:
1) Corrects the detection of whether a multi-segment buffer is
still tracking data.
2) Clears all the buffer log formats for a multi-segment buffer.
Signed-off-by: Mark Tinguely <tinguely@sgi.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Ben Myers <bpm@sgi.com>