Add mp2a fourCC for some Mpeg Audio

(cherry picked from commit 18d3b924)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

src/misc/fourcc.c

@@ -969,6 +969,7 @@ static const entry_t p_list_audio[] = {
     /* MPEG Audio layer 1/2/3 */
     B(VLC_CODEC_MPGA, "MPEG Audio layer 1/2/3"),
         A("mpga"),
+        A("mp2a"),
         A(".mp1"),
         A(".mp2"),
         A("mp3 "),