Correct the comment about the partition context
Correct the comment about the partition context

Since av1 has added 128x128 SuperBlock to prevous 64x64,
it now needs one more bit to represent partition context
as a bitfield.

Change-Id: I793279d1d73176c8f157e4e868ae66a2ac16dc7c

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom