V4L/DVB (9172): S2API: Bugfix related to DVB-S / DVB-S2 tuning for the legacy API.

Fixes switching from S2API to legacy where legacy params given to S2API
aware demods are cached ones and not those implied in the legacy API.

It was found (on an S2API aware demod at least) that after using
an S2API aware application and then switching to a legacy application
that prior S2API params were in effect were legacy has only
implied values. This fixes this.

Signed-off-by: Darron Broad <darron@kewl.org>
Signed-off-by: Steven Toth <stoth@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>