libavcodec: Add missing AVClass pointers

This fixes crashes since 243df135.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/alacenc.c

@@ -59,6 +59,7 @@ typedef struct AlacLPCContext {
 } AlacLPCContext;
 
 typedef struct AlacEncodeContext {
+    const AVClass *class;
     AVCodecContext *avctx;
     int frame_size;                     /**< current frame size               */
     int verbatim;                       /**< current frame verbatim mode flag */

libavcodec/huffyuv.h

@@ -59,6 +59,7 @@ typedef enum Predictor {
 } Predictor;
 
 typedef struct HYuvContext {
+    const AVClass *class;
     AVCodecContext *avctx;
     Predictor predictor;
     GetBitContext gb;

libavcodec/utvideo.h

@@ -65,6 +65,7 @@ extern const int ff_ut_pred_order[5];
 extern const int ff_ut_rgb_order[4];
 
 typedef struct UtvideoContext {
+    const AVClass *class;
     AVCodecContext *avctx;
     BswapDSPContext bdsp;
     HuffYUVEncDSPContext hdsp;