media: lgdt330x: provide DVBv5 Carrier S/N measurements

Change the logic at the driver to provide CNR stats via
DVBv5 API.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>