correctly decrement numToWake to avoid waking more

Change-Id: I2a0e5f2bb38a0d8831a05028b89bee98fa48c22a
Reviewed-on: http://review.couchbase.org/40154
Tested-by: Sundararaman Sridharan <sundar@couchbase.com>
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>