libshine: fix support for shine 3.0

shine_encode_buffer expects written to be an int pointer, while the
previous shine_encode_frame expected it to be a long pointer.

Thus encoding with libshine currently always fails with
"internal buffer too small", because a negative return value of
shine_encode_buffer is interpreted as a very large long value.
Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavcodec/libshine.c

@@ -71,7 +71,7 @@ static int libshine_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
     SHINEContext *s = avctx->priv_data;
     MPADecodeHeader hdr;
     unsigned char *data;
-    long written;
+    int written;
     int ret, len;
 
     if (frame)