libusb: Update to 1.0.20

libusb: Update to 1.0.20

* Add Haiku support
* Fix multiple memory and resource leaks (#16, #52, #76, #81)
* Fix possible deadlock when executing transfer callback
* New libusb_free_pollfds() API
* Linux: Allow larger isochronous transfer submission (#23)
* Examples: Add two-stage load support to fxload (#12)
* Correctly report cancellations due to timeouts
* Improve efficiency of event handling
* Improve speed of transfer submission in multi-threaded environments
* Various other bug fixes and improvements

Signed-off-by: Alexander Marx <alexander.marx@ipfire.org>