[media] ngene: Improved channel initialisation and release

Refactored code for channel initialisation and release:
- Do not create device nodes which are not required.
- Better error handling.

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