dvdsubdec: fix incorrect colors.

dvdsubdec: fix incorrect colors.

On DVD and HD-DVD colors are stored in the order YCrCb (and not YCbCr) as mentioned in the specifications:
see DVD Specifications for Read-Only Disc / Part 3, 4.3 Program Chain Information (7) PGC_SP_PLT
see DVD Specifications for High Definition Disc, 5.2 Navigation for Standard Content (11) PGC_SDSP_PLT
see DVD Specifications for High Definition Disc, 5.2 Navigation for Standard Content (12) PGC_HDSP_PLT
see DVD Specifications for High Definition Disc, 5.5 Presentation Data (4) SET_COLOR2

When decoding a DVD or HD-DVD subtitle, the colors were incorrectly set.

Signed-off-by: Anton Khirnov <anton@khirnov.net>