[media] ngene: Clean-up driver initialisation (part 1)

If tuner initialisation failed, the frontend node was not removed.
When the frontend was opened, a kernel oops occurred...

This is the first step to improve error handling during initialisation.

Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>