V4L/DVB (9170): cx24116: Sanity checking to data input via S2API to the cx24116 demod.

Add some sanity checking to data input via S2API to the cx24116 demod.
This patch is valid for both s2-mfe and s2.

It was found when testing KAFFEINE with S2API support that invalid
modulation modes amongst other parameters were being delivered to
the demod. In order to debug this sanity checking has been added.

An example session would involve kaffeine setting QAM_AUTO when
querying DVB-T, then later when trying to tune to DVB-S this
cached value would be presented in error.

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>