gallium/i965: added const to silence warnings

src/gallium/drivers/i965simple/brw_context.h

@@ -504,7 +504,7 @@ struct brw_context
       /* Arrays with buffer objects to copy non-bufferobj arrays into
        * for upload:
        */
-      struct pipe_vertex_buffer *vbo_array[PIPE_ATTRIB_MAX];
+      const struct pipe_vertex_buffer *vbo_array[PIPE_ATTRIB_MAX];
 
       struct brw_vertex_element_state inputs[PIPE_ATTRIB_MAX];