USB: serial: ftdi_sio: Annotate the current Xsens PID assignments

commit 9273b8a2 upstream.

The converters are used in specific products. It can be useful to know
which they are exactly.

Signed-off-by: Patrick Riphagen <patrick.riphagen@xsens.com>
Signed-off-by: Frans Klaver <frans.klaver@xsens.com>
Cc: Johan Hovold <johan@kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>