avcodec/sbrdsp_fixed: Fix integer overflow in sbr_hf_apply_noise()

Fixes: runtime error: signed integer overflow: -2049425300 + -117591631 cannot be represented in type 'int'
Fixes: part of 2096/clusterfuzz-testcase-minimized-4901566068817920

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

libavcodec/sbrdsp_fixed.c

@@ -264,8 +264,8 @@ static av_always_inline int sbr_hf_apply_noise(int (*Y)[2],
     int m;
 
     for (m = 0; m < m_max; m++) {
-        int y0 = Y[m][0];
-        int y1 = Y[m][1];
+        unsigned y0 = Y[m][0];
+        unsigned y1 = Y[m][1];
         noise = (noise + 1) & 0x1ff;
         if (s_m[m].mant) {
             int shift, round;