Fix leak in failure path of libusb_get_max_packet_size()

If libusb_get_max_packet_size() or libusb_get_max_iso_packet_size()
fails to find the endpoint, it leaks the configuration descriptor.  Fix
this.

Signed-off-by: John Sheu <sheu@google.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
libusb 1.0.19

Signed-off-by: Hans de Goede <hdegoede@redhat.com>