glsl: Use typed foreach_in_list instead of foreach_list.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/builtin_functions.cpp

@@ -2575,8 +2575,7 @@ builtin_builder::call(ir_function *f, ir_variable *ret, exec_list params)
 {
    exec_list actual_params;
 
-   foreach_list(node, &params) {
-      ir_variable *var = (ir_variable *) node;
+   foreach_in_list(ir_variable, var, &params) {
       actual_params.push_tail(var_ref(var));
    }