USB: serial: cp210x: added Ketra N1 wireless interface support

commit bfc2d7dfdd761ae3beccdb26abebe03cef042f46 upstream.

Added support for Ketra N1 wireless interface, which uses the
Silicon Labs' CP2104 USB to UART bridge with customized PID 8946.

Signed-off-by: Joe Savage <joe.savage@goketra.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>