TT#14008 eliminate compiler warning

AVCodec * has been decorated with "const" in newer versions of ffmpeg.

Change-Id: I999f1aba761a5687067a603d76b93b07e5ec91a3

lib/codeclib.c

@@ -590,7 +590,7 @@ const codec_def_t *codec_find_by_av(enum AVCodecID id) {
 
 
 static const char *avc_decoder_init(decoder_t *dec, const str *fmtp, const str *extra_opts) {
-	AVCodec *codec = dec->def->decoder;
+	const AVCodec *codec = dec->def->decoder;
 	if (!codec)
 		return "codec not supported";
 

lib/codeclib.h

@@ -164,8 +164,8 @@ struct codec_def_s {
 	const codec_type_t *codec_type;
 
 	// libavcodec
-	AVCodec *encoder;
-	AVCodec *decoder;
+	const AVCodec *encoder;
+	const AVCodec *decoder;
 };
 
 struct format_s {
@@ -250,7 +250,7 @@ struct encoder_s {
 
 	union {
 		struct {
-			AVCodec *codec;
+			const AVCodec *codec;
 			AVCodecContext *avcctx;
 
 			union {