LU-15268 mdt: reveal the real intent close error code

LU-15268 mdt: reveal the real intent close error code

mdt_mfd_close() clobbers the intent close error so that user space
tool only knows that the close intent hasn't finished and reports
-EBUSY instead of the real error code.

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I72f474a73e8b73cdc35ca38eaaec5af182f63ca7
Reviewed-on: https://review.whamcloud.com/45636
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Peter Jones <pjones@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>