[media] tuner: Fix numberspace conflict between xc4000 and pti 5nf05 tuners

Update xc4000 tuner definition, number 81 is already in use by
TUNER_PARTSNIC_PTI_5NF05.

Cc: stable@kernel.org
Signed-off-by: Miroslav Slugen <thunder.mmm@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>