usb.sch cleanup.
usb.sch cleanup.

- usb.sch: labeled D+ and D- nets
- usb.sch: moved VDD to avoid connected cross intersection

cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan