cosmetics: Fix spelling mistakes

Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavformat/mpeg.c

@@ -1,5 +1,5 @@
 /*
- * MPEG1/2 demuxer
+ * MPEG-1/2 demuxer
  * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
  *
  * This file is part of Libav.
@@ -287,7 +287,7 @@ redo:
             goto error_redo;
         c = avio_r8(s->pb);
         len--;
-        /* XXX: for mpeg1, should test only bit 7 */
+        /* XXX: for MPEG-1, should test only bit 7 */
         if (c != 0xff)
             break;
     }