nir: Actually propagate progress in nir_opt_move_load_ubo.

Found with Jasons new metadata rework (https://gitlab.freedesktop.org/mesa/mesa/merge_requests/950).

Fixes: af355aaa07 "nir: add nir_opt_move_load_ubo() optimization pass"
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/nir/nir_opt_move_load_ubo.c

@@ -91,7 +91,7 @@ move_load_ubo(nir_block *block)
       }
    }
 
-   return false;
+   return progress;
 }
 
 bool