Fix unsubscripted-variable case of to_batched (reported by Marmaduke Woodman)

loopy/transform/batch.py

@@ -73,7 +73,7 @@ class _BatchVariableChanger(RuleAwareIdentityMapper):
         if not self.needs_batch_subscript(expr.name):
             return super(_BatchVariableChanger, self).map_variable(expr, expn_state)
 
-        return expr.aggregate[self.batch_iname_expr]
+        return expr[self.batch_iname_expr]
 
 
 def _add_unique_dim_name(name, dim_names):