Return TypedData_Wrap_Struct directly.

Change-Id: I6cf77f01370204ad4bc7b345a040a9a3de1706a0
diff --git a/ruby/ext/google/protobuf_c/map.c b/ruby/ext/google/protobuf_c/map.c
index 5043f39..92fc728 100644
--- a/ruby/ext/google/protobuf_c/map.c
+++ b/ruby/ext/google/protobuf_c/map.c
@@ -167,10 +167,9 @@
 
 VALUE Map_alloc(VALUE klass) {
   Map* self = ALLOC(Map);
-  VALUE ret = TypedData_Wrap_Struct(klass, &Map_type, self);
   memset(self, 0, sizeof(Map));
   self->value_type_class = Qnil;
-  return ret;
+  return TypedData_Wrap_Struct(klass, &Map_type, self);
 }
 
 static bool needs_typeclass(upb_fieldtype_t type) {