[NFC] simplify matching

Author: ZuseZ4

compiler/rustc_codegen_llvm/src/builder/autodiff.rs

@@ -240,14 +240,8 @@ fn generate_enzyme_call<'ll>(
         args.push(fn_to_diff);
 
         let enzyme_primal_ret = cx.create_metadata("enzyme_primal_return".to_string()).unwrap();
-        match output {
-            DiffActivity::Dual => {
-                args.push(cx.get_metadata_value(enzyme_primal_ret));
-            }
-            DiffActivity::Active => {
-                args.push(cx.get_metadata_value(enzyme_primal_ret));
-            }
-            _ => {}
+        if matches!(attrs.ret_activity, DiffActivity::Dual | DiffActivity::Active) {
+            args.push(cx.get_metadata_value(enzyme_primal_ret));
         }
 
         let outer_args: Vec<&llvm::Value> = get_params(outer_fn);