Modify fourcc to accept DXSA subtitles

but VLC still can't decode these subtitles
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

src/misc/fourcc.c

@@ -1537,6 +1537,7 @@ static const staticentry_t p_list_spu[] = {
         A("XSUB"),
         A("xsub"),
         A("DXSB"),
+        A("DXSA"),
 
     B(VLC_CODEC_SSA, "SubStation Alpha subtitles"),
         A("ssa "),