MB-100: fix XDCR dialyzer error

Change-Id: I2c8c3a2e40573d0a611cf037459ff044c9c2c292
Reviewed-on: http://review.couchbase.org/28544
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Junyi Xie <junyi.couchbase@gmail.com>