mesa: Use VertexArray, not _VertexArray, in array size expressions.

Both sizes are VERT_ATTRIB_MAX, so this has no effect.  But it drops a
few trivial uses of the derived state.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Fredrik Höglund <fredrik@kde.org>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/main/arrayobj.c

@@ -230,7 +230,7 @@ _mesa_initialize_vao(struct gl_context *ctx,
    obj->RefCount = 1;
 
    /* Init the individual arrays */
-   for (i = 0; i < Elements(obj->_VertexAttrib); i++) {
+   for (i = 0; i < Elements(obj->VertexAttrib); i++) {
       switch (i) {
       case VERT_ATTRIB_WEIGHT:
          init_array(ctx, obj, VERT_ATTRIB_WEIGHT, 1, GL_FLOAT);