pgssubdec: fix incorrect colors.

On Blu-ray colors are stored in the order YCrCb (and not YCbCr) as mentioned in the specifications:
see System Description Blu-ray Disc Read-Only Format, 9.14.4.2.2.1 Palette Definition Segment

When decoding a Blu-ray subtitle, the colors were incorrectly set.
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/pgssubdec.c

@@ -246,8 +246,8 @@ static void parse_palette_segment(AVCodecContext *avctx,
     while (buf < buf_end) {
         color_id  = bytestream_get_byte(&buf);
         y         = bytestream_get_byte(&buf);
-        cb        = bytestream_get_byte(&buf);
         cr        = bytestream_get_byte(&buf);
+        cb        = bytestream_get_byte(&buf);
         alpha     = bytestream_get_byte(&buf);
 
         YUV_TO_RGB1(cb, cr);