The only caller that ever sets it can call fsync_bdev itself easily.  Also
update some comments.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Cc: <viro@parcelfarce.linux.theplanet.co.uk>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>