mkvmuxer: Fix bits per channel in the colour element.
mkvmuxer: Fix bits per channel in the colour element.

Never written: copy/paste error + patch size eye glazing.

Change-Id: I2c5295b26427e0ce254b88c8b4cb5106a5f37258

webmproject/libwebm,webmproject/libwebm,webmproject/libwebm