swresample/dither: use av_malloc_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswresample/dither.c

@@ -26,7 +26,7 @@
 void swri_get_dither(SwrContext *s, void *dst, int len, unsigned seed, enum AVSampleFormat noise_fmt) {
     double scale = s->dither.noise_scale;
 #define TMP_EXTRA 2
-    double *tmp = av_malloc((len + TMP_EXTRA) * sizeof(double));
+    double *tmp = av_malloc_array(len + TMP_EXTRA, sizeof(double));
     int i;
 
     for(i=0; i<len + TMP_EXTRA; i++){