V4L/DVB (13340): stv0900: big rework to support cut 3.0.

Patch 3 of 4.
Also patch changes logic to prevent code repetitions and big indents.
It makes checkpatch silent :)

Signed-off-by: Igor M. Liplianin <liplianin@netup.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>