The mpio dereference should be moved below the BUG_ON NULL test
in multipath_end_io().

spatch with a semantic match was used to found this.
(http://coccinelle.lip6.fr/)
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>