dm bufio: use list_move

Use list_move() instead of list_del() + list_add().

spatch with a semantic match was used to find this.
(http://coccinelle.lip6.fr/

)

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>