mesa: replace MALLOC w/ CALLOC to fix valgrind warning

src/mesa/main/arrayobj.c

@@ -77,7 +77,7 @@ lookup_arrayobj(GLcontext *ctx, GLuint id)
 struct gl_array_object *
 _mesa_new_array_object( GLcontext *ctx, GLuint name )
 {
-   struct gl_array_object *obj = MALLOC_STRUCT(gl_array_object);
+   struct gl_array_object *obj = CALLOC_STRUCT(gl_array_object);
    if (obj)
       _mesa_initialize_array_object(ctx, obj, name);
    return obj;