glsl: Report progress from opt_copy_propagation_elements().

It's been altering the tree and reporting "false" since January 2011.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/glsl/opt_copy_propagation_elements.cpp

@@ -288,6 +288,7 @@ ir_copy_propagation_elements_visitor::handle_rvalue(ir_rvalue **ir)
 					source_chan[2],
 					source_chan[3],
 					chans);
+   progress = true;
 
    if (debug) {
       printf("to:\n");