libswr/rematrix: add braces to silence a warning.

Signed-off-by: Nicolas George <nicolas.george@normalesup.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswresample/rematrix.c

@@ -83,7 +83,7 @@ static int sane_layout(int64_t layout){
 
 int swr_rematrix_init(SwrContext *s){
     int i, j, in_i, out_i;
-    double matrix[64][64]={0};
+    double matrix[64][64]={{0}};
     int64_t unaccounted= s->in_ch_layout & ~s->out_ch_layout;
     double maxcoef=0;