avformat/spdifdec: Use 64bit to compute bit rate

Fixes: signed integer overflow: 32 * 553590816 cannot be represented in type 'int'
Fixes: 50993/clusterfuzz-testcase-minimized-ffmpeg_dem_WAV_fuzzer-6564974517944320

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/spdifdec.c

@@ -226,7 +226,7 @@ int ff_spdif_read_packet(AVFormatContext *s, AVPacket *pkt)
     if (!s->bit_rate && s->streams[0]->codecpar->sample_rate)
         /* stream bitrate matches 16-bit stereo PCM bitrate for currently
            supported codecs */
-        s->bit_rate = 2 * 16 * s->streams[0]->codecpar->sample_rate;
+        s->bit_rate = 2 * 16LL * s->streams[0]->codecpar->sample_rate;
 
     return 0;
 }