Fix libusb20_dev_get_desc(3) to use the "vendor product" order, not
"product vendor". This is consistent with how it's generally done.
The ordering is visible eg in usbconfig(8) output.

Note to self: MFC this to 9 and 8.

Reviewed by: hselasky@
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D8258