docs: fix a NameError in querying.rst

Author: allan-cedric

docs/usage/querying.rst

@@ -45,7 +45,7 @@ Print unique identification (Id) of all employees with name John Smith:
     smith_employees_request = northwind.entity_sets.Employees.get_entities()
     smith_employees_request = smith_employees_request.filter("FirstName eq 'John' and LastName eq 'Smith'")
 
-    for smith in smith_employees.execute():
+    for smith in smith_employees_request.execute():
         print(smith.EmployeeID)