LU-4430 mdt: check for MDS_FMODE_EXEC in mdt_mfd_open()

In the error path of mdt_mfd_open() check for MDS_FMODE_EXEC rather
than FMODE_EXEC in the open flags.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I04c53eb1af0fdeeb2c2b0c2f2ef1340b247921d8
Reviewed-on: http://review.whamcloud.com/8719
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>