It's only used for one kind of move, so make that explicit.  Also clean
up the code a bit by using list_for_each_safe.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NShaohua Li <shli@fb.com>
Signed-off-by: NNeilBrown <neilb@suse.com>