USB: sierra: add 1199:68AA device ID

This VID:PID is used for some Direct IP devices behaving
identical to the already supported 0F3D:68AA devices.

Cc: <stable@vger.kernel.org>
Reported-by: Lars Melin <larsm17@gmail.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Johan Hovold <johan@kernel.org>