serial_hid: improve and tighten "find USB" for the HID transport

serial_hid: improve and tighten "find USB" for the HID transport

The .find_usb() method of the HID transport previously returned
connections which lacked the "hid/" prefix and chip type, thus could
later not be used with open() and data communication calls. Add the
missing decoration.

As a minor optimization, lookup the chip type and name from the caller's
VID:PID pair already if it's specific enough, still lookup the chip for
every enumerated device if the caller's VID:PID pair is unspecific.

Tighten the result set of the HID transport's USB search. Only return
connections which involve one of the supported chips. The other devices
very probably cannot be used to connect to measurement equipment anyway,
listing mice and keyboards and other unrelated stuff was found to be not
so useful.