Fix using r instead of v

Author: josh11b

proposals/p3720.md

@@ -340,8 +340,8 @@ v.F() == v.(C.F)()
 r.F() == r.(C.F)()
       == r.(__C_F)()
       == (*__C_F.((__TypeOf_C_F as RefBind(C)).Op(&r)))()
-      == (*(&v as __RefBind_C_F*))()
-      == (*(&v as __RefBind_C_F*)).(Call(()).Op)()
+      == (*(&r as __RefBind_C_F*))()
+      == (*(&r as __RefBind_C_F*)).(Call(()).Op)()
 ```
 
 > **Note:** This rewrite results in a method call, but the rewrite is only