platform/x86: intel_cht_int33fe: Convert to use set_secondary_fwnode()

In one place we open coded set_secondary_fwnode().
Let's replace it with a helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>