[USBPORT] Correctly find interface descriptor in USBPORT_ParseConfigurationDescriptor

[USBPORT] Correctly find interface descriptor in USBPORT_ParseConfigurationDescriptor

There can be other descriptors between the config descriptor and the
first interface descriptor, so we specifically need to check for
the interface descriptor type and skip anything before that.
We also need to guard against bLength == 0, which would cause an
infinite loop, instead of doing a second bDescriptorType check.