Add a context to av_log() call and update the trace not to be redundant.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@17380 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/mm.c

@@ -168,7 +168,7 @@ static int mm_read_packet(AVFormatContext *s,
             return 0;
 
         default :
-            av_log(NULL, AV_LOG_INFO, "mm: unknown chunk type 0x%x\n", type);
+            av_log(s, AV_LOG_INFO, "unknown chunk type 0x%x\n", type);
             url_fseek(pb, length, SEEK_CUR);
         }
     }