Just return ok from sync().

Change-Id: I63d4bb6dac32edda758f38f475cbd7cc5ab1ecf9
Reviewed-on: http://review.couchbase.org/37515
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>