nir/divergence: change nir_has_divergent_loop() to return true only for divergent breaks

The important information is whether a loop has a uniform number
of iterations.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28627>

src/compiler/nir/nir_divergence_analysis.c

@@ -1477,7 +1477,7 @@ nir_has_divergent_loop(nir_shader *shader)
 
    foreach_list_typed(nir_cf_node, node, node, &func->body) {
       if (node->type == nir_cf_node_loop) {
-         if (nir_loop_is_divergent(nir_cf_node_as_loop(node)))
+         if (nir_cf_node_as_loop(node)->divergent_break)
             return true;
       }
    }