LU-657 obdfilter: fix bug in previous patch

LU-657 obdfilter: fix bug in previous patch

in the merged patch http://review.whamcloud.com/#change,3446,
the usage of fsfilt_commit_wait is wrong, and it doesn't stop
the journal firstly.

Signed-off-by: Hongchao Zhang <hongchao.zhang@whamcloud.com>
Change-Id: I3a36edf7049466880c27c14bb7f99966aa75d4f1
Reviewed-on: http://review.whamcloud.com/3692
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>