winusb: Check for ClassGuid changes on re-enumeration

Previously only the dev_id (VID/PID/serial) was checked, but if the
bcdDevice has changed, Windows will have re-enumerated the device and
possibly attributed another ClassGuid to it.

Fixes issue #897.
Closes #900

Thanks to Craig Hutchinson for reporting, suggestion and testing.

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>
Signed-off-by: Nathan Hjelm <hjelmn@google.com>