avformat/acm: use ff_get_extradata()

libavformat/acm.c

@@ -44,12 +44,9 @@ static int acm_read_header(AVFormatContext *s)
     st->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
     st->codecpar->codec_id   = AV_CODEC_ID_INTERPLAY_ACM;
 
-    ff_alloc_extradata(st->codecpar, 14);
-    if (!st->codecpar->extradata)
-        return AVERROR(ENOMEM);
-    ret = avio_read(s->pb, st->codecpar->extradata, 14);
-    if (ret < 10)
-        return ret < 0 ? ret : AVERROR_EOF;
+    ret = ff_get_extradata(s, st->codecpar, s->pb, 14);
+    if (ret < 0)
+        return ret;
 
     st->codecpar->channels    = AV_RL16(st->codecpar->extradata +  8);
     st->codecpar->sample_rate = AV_RL16(st->codecpar->extradata + 10);