I.e. we render the same area as one larger tile, and then
as 4 sub-tiles (which, when put together, should be identical
to the larger tile). However currently only the top-left sub-tile
actually matches the larger tile, so we have to disable the test
for the remaining sub-tiles.

Change-Id: If1130022b43898e20fefff3e9f592102da3e413a