parse.y: fix rb_str_symname_type call

* parse.y (rb_str_dynamic_intern): fix the second argument to
  rb_str_symname_type, which is a bit mask but not a boolean.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45434 b2dd03c8-39d4-4d8f-98ff-823fe69b080e