avcodec/mpegaudiodec_template: Fix multiple runtime error: signed integer overflow

Fixes: 648/clusterfuzz-testcase-5337961317007360

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

libavcodec/mpegaudiodec_template.c

@@ -459,7 +459,7 @@ static av_cold int decode_init(AVCodecContext * avctx)
    cases. */
 static void imdct12(INTFLOAT *out, INTFLOAT *in)
 {
-    INTFLOAT in0, in1, in2, in3, in4, in5, t1, t2;
+    SUINTFLOAT in0, in1, in2, in3, in4, in5, t1, t2;
 
     in0  = in[0*3];
     in1  = in[1*3] + in[0*3];