usb: plusb: Add support for National Instruments host-to-host cable

The National Instruments USB Host-to-Host Cable is based on the Prolific
PL-25A1 chipset.  Add its VID/PID so the plusb driver will recognize it.

Signed-off-by: Ben Shelton <ben.shelton@ni.com>
Signed-off-by: David S. Miller <davem@davemloft.net>