[media] stb0899: store autodetected inversion while tuning in non S2 mode

In non S2 mode, the device is able to autodetect inversion. So
let's store it for tuning to S2 transponders.

Signed-off-by: Reinhard Nißl <rnissl@gmx.de>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>