Fix the broken unit test when ext-tile and obu are both turned on.
The test failure was due to the merge of CONFIG_ADD_4BYTES_OBUSIZE.
This solves the unit test failure cases when cm->large_scale_tile
is on.

BUG=aomedia:1179

Change-Id: I7b4a5720e493db2a7d914fc9f8b886a67b1e85cd