Add 'const' to pointer parameters

test/testgpu_spinning_cube.c

@@ -152,7 +152,7 @@ perspective_matrix(float fovy, float aspect, float znear, float zfar, float *r)
  * major. In-place multiplication is supported.
  */
 static void
-multiply_matrix(float *lhs, float *rhs, float *r)
+multiply_matrix(const float *lhs, const float *rhs, float *r)
 {
     int i, j, k;
     float tmp[16];