PCBC-240: Fixup API descr of return value for touch

Change-Id: I6e2140d2212af5b967bb424ba7346ed792e4d3dd
Reviewed-on: http://review.couchbase.org/28568
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>