avformat/oggparseopus: fix nb_headers

Line comes from ecab1c77
and was not merged previously

Thanks-to: Nicolas George <george@nsup.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/oggparseopus.c

@@ -140,4 +140,5 @@ const struct ogg_codec ff_opus_codec = {
     .magicsize        = 8,
     .header           = opus_header,
     .packet           = opus_packet,
+    .nb_header        = 1,
 };