V4L/DVB (5247): Stv0297: Enable BER/UNC counting

Enable BER/UNC counting for the stv0297 frontend.
The idea for this patch comes from stv0297_cs.c.

Signed-off-by: Hartmut Birr <e9hack@googlemail.com>
Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>