V4L/DVB (13974): [STV090x] Fix locking reliabilty issues in automatic mode.

In automatic S/S2 detection mode, locking of a DVB-S transponder could
fail when coming from a DVB-S2 transponder. This change fixes the issue
by first disabling DVB-S and DVB-S2 mode before enabling it again.

Signed-off-by: Andreas Regel <andreas.regel@gmx.de>
Signed-off-by: Manu Abraham <manu@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>