MB-9953 Correct a rev_seqno type to uint64_t

Change-Id: I46afadda87a83bf5f1b01dcb007b2a0feb6a7e27
Reviewed-on: http://review.couchbase.org/32775
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>