Set bits_per_coded_sample when encoding Y41P.

This allows mplayer -vc bt411 to decode files
encoded with FFmpeg.

Reviewed-by: Paul B Mahol

libavcodec/y41penc.c

@@ -30,6 +30,7 @@ static av_cold int y41p_encode_init(AVCodecContext *avctx)
     }
 
     avctx->coded_frame = avcodec_alloc_frame();
+    avctx->bits_per_coded_sample = 12;
 
     if (!avctx->coded_frame) {
         av_log(avctx, AV_LOG_ERROR, "Could not allocate frame.\n");