If save_raid_disk is >= 0, then the device could be a device that is
already in sync that is being re-added.  So we need to default this
value to -1.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>