HID: logitech-hidpp: Reconcile USB and Unifying serials

HID: logitech-hidpp: Reconcile USB and Unifying serials

Now that USB HID++ devices can gather a serial number that matches the
one that would be gathered when connected through a Unifying receiver,
remove the last difference by dropping the product ID as devices
usually have different product IDs when connected through USB or
Unifying.

For example, on the serials on a G903 wired/wireless mouse:
- Unifying before patch: 4067-e8-ce-cd-45
- USB before patch: c086-e8-ce-cd-45
- Unifying and USB after patch: e8-ce-cd-45

Signed-off-by: Bastien Nocera <hadess@hadess.net>
Link: https://lore.kernel.org/r/20230302130117.3975-2-hadess@hadess.net
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>