media: cx231xx: get rid of videobuf-dvb dependency

This driver doesn't use videobuf-dvb. So, stop adding an
unused struct and unused header on it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>