Fix: matrix benchmark uses wrong size parameters.

extern/benchmark_base/include/benchmark_base/matrix.h

@@ -20,8 +20,8 @@ class matrix {
   T data[SIZE][SIZE];
   T data[SIZE][SIZE];
 
 
   explicit matrix() {
   explicit matrix() {
-    for (int i = 0; i < MATRIX_SIZE; i++) {
-      for (int j = 0; j < MATRIX_SIZE; j++) {
+    for (int i = 0; i < SIZE; i++) {
+      for (int j = 0; j < SIZE; j++) {
         data[i][j] = i;
         data[i][j] = i;
       }
       }
     }
     }