USB: cdc-acm: add device id for GW Instek AFG-2225

Add device-id entry for GW Instek AFG-2225, which has a byte swapped
bInterfaceSubClass (0x20).

Reported-by: Karl Palsson <karlp@tweak.net.au>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>