LU-534 mds: correct assertion

LU-534 mds: correct assertion

Orphan inode can be reached on mds_open when opening by fid which
takes place on accessing files via nfs correct the assertion
correspondingly.

Bugzilla: 17764
Author: Vladimir Saveliev <vladimir.saveliev@oracle.com>
Signed-off-by: Vladimir Saveliev <vladimir.saveliev@oracle.com>
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: Id6cde949003c722b56fe7ccec43b2d8b8a0667bb
Reviewed-on: http://review.whamcloud.com/1894
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>