md-cluster: Allow spare devices to be marked as faulty

If a spare device was marked faulty, it would not be reflected
in receiving nodes because it would mark it as activated and continue.
Continue the operation, so it may be set as faulty.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: NeilBrown <neilb@suse.com>