test: wrok around PSB behavior on vp8vldemo

normalize slice_data_offset to 0 and macroblock_offset to [0,7]

Change-Id: Ifa30080dc8df3b7821bea7f36a4f62dd730a6797
Merge pull request #2 from 01org/halley

test: wrok around PSB behavior on vp8vldemo