MB-12476: Set reduce correctly

The reduce in the spatial views is the original MBB (needed by the
RR*-tree allgorithm).

Change-Id: Ia566633a1b814e5e2df676f6c4ff8455ed10caac
Reviewed-on: http://review.couchbase.org/42755
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>