Fix compile warning from clang

Change-Id: If5bfed8fd995f4feeceafe4f6cd618e5a259dd81
Reviewed-on: http://review.couchbase.org/40488
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>