Setting chroma_qp to 0 for PCM blocks is really an interesting minor

Setting chroma_qp to 0 for PCM blocks is really an interesting minor
optimization, more interresting would it have been had the author
thought about what value chroma_qp would have for the following MB.
Or failing that, had actually tested the code.
So this reverts this non-functional optimization, and makes the code work.
Fixes at least CAPM3_Sony_D.jsv

Originally committed as revision 14335 to svn://svn.ffmpeg.org/ffmpeg/trunk