usb: typec: class: Don't use port parent for getting mux handles

It is not possible to use the parent of the port device when
requesting mux handles as the parent may be a multiport USB
Type-C or PD controller. The muxes must be assigned to the
ports, not the controllers.

This will also move the requesting of the muxes after the
port device is initialized.

Acked-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>