media: lgdt3306a: Add CNR v5 stat

The CNR is already calculated, so populate DVBv5 CNR stat
during read_status.

Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>