encoding.c: use rb_check_arity

* encoding.c (enc_dump): use rb_check_arity to just check number
  of arguments.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52854 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

encoding.c

@@ -1268,7 +1268,7 @@ enc_compatible_p(VALUE klass, VALUE str1, VALUE str2)
 static VALUE
 enc_dump(int argc, VALUE *argv, VALUE self)
 {
-    rb_scan_args(argc, argv, "01", 0);
+    rb_check_arity(argc, 0, 1);
     return enc_name(self);
 }