V4L/DVB (12486): cx88: fix TBS 8920 card support

It does matter to set explicitly gpio0 value in
cx88_board structure for TBS 8920 card.

Signed-off-by: Igor M. Liplianin <liplianin@me.by>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>