avcodec/r210enc: Use av_rescale for bitrate

Fixes: signed integer overflow: 281612954574848 * 65344 cannot be represented in type 'long'
Fixes: 68956/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_R210_fuzzer-6459074458746880

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

libavcodec/r210enc.c

@@ -35,7 +35,7 @@ static av_cold int encode_init(AVCodecContext *avctx)
 
     avctx->bits_per_coded_sample = 32;
     if (avctx->width > 0)
-        avctx->bit_rate = ff_guess_coded_bitrate(avctx) * aligned_width / avctx->width;
+        avctx->bit_rate = av_rescale(ff_guess_coded_bitrate(avctx), aligned_width, avctx->width);
 
     return 0;
 }