Fix uncorrected block counter and bit error rate to follow DVB API spec:
- Unsupported controls return -ENOSYS.
- UNC must never be set to 0.

Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>