MB-7656 Fix function return value to void

void * was useless, likely a typo.

Change-Id: I82e3aa4e59452f649b88cef71d6fc25398d345a6
Reviewed-on: http://review.couchbase.org/25598
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Fulu Li <fulu@couchbase.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>