V4L/DVB (7463): cx88: Enable color killer by default

An enabled color killer will not degrade picture quality for color
input signals, only suppress bogus color information on
black-and-white input. Therefore enable it by default.

Signed-off-by: Frej Drejhammar <frej.drejhammar@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>