All the example code are indented with four spaces except this one.

Fix this by adding four spaces here.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20190304071631.27567-3-richardw.yang@linux.intel.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>