we have the resource on the stack, so just use it

We don't need to ask `scope` for the resource because we already have it
right here.

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -1692,7 +1692,7 @@ def resource_scope(kind, resource) #:nodoc:
             @nesting.push(resource)
 
             with_scope_level(kind) do
-              controller_scope(parent_resource.resource_scope) { yield }
+              controller_scope(resource.resource_scope) { yield }
             end
           ensure
             @nesting.pop