V4L/DVB (5420): Initialize the inputs before registering the devices.

Once the devices have been registered anyone can start changing the inputs or
TV standard before they have been initialized by the driver. This leads to
cases were the input is changed in an udev rule, but after that rule is
triggered the tail-end of the ivtv driver initialization can override
that by selecting the tuner input.
The correct sequence is to first setup the input, initial frequency and TV
standard before finally registering the video devices. This prevents any
udev rules from being triggered prematurely.

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