V4L/DVB: tvaudio: remove obsolete tda8425 initialization

The tda8425 initialization function sets up the inputmap for riva boards.
After some digging I discovered that this was for the V4L rivatv driver
that is found on sourceforge. This driver hasn't been maintained since the
last 5 years and will no longer work with the current v4l framework.

So we can safely remove this.

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