ParseVpxCodecPrivate: fix chroma subsampling parsing

1 is defined as 4:2:0 colocated with luma (0,0):
https://www.webmproject.org/docs/container/#vp9-codec-feature-metadata-codecprivate

Change-Id: I983d7591bbdf60a6ff0b512b0a3a6b1d313589c7
2 files changed