Mute compile warning from gcc

Change-Id: If9babaf57436ce0b107d01dd1017b4a4b5ccd13d
Reviewed-on: http://review.couchbase.org/43022
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>