cx18-cards.h had a copy of the audio and video input enums
from cx18-av-core.h, but with different prefixes. Removed
that copy and used the ones from cx18-av-core.h.

Thanks to Andy Walls <awalls@radix.net> for the report.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>