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.

Lustre-change: https://review.whamcloud.com/45636
Lustre-commit: TBD (from dc6dee1f5683ac91d637533b4c220617f62e60d2)

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I72f474a73e8b73cdc35ca38eaaec5af182f63ca7
Reviewed-on: https://review.whamcloud.com/46092
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>