[media] tuner-core: return the frequency range of the correct tuner

The frequency range of the current tuner (radio or TV) was returned
instead of the frequency range of the requested tuner (which depends
on the device node).

This bug caused the frequency range of the radio tuner to be returned
when G_TUNER was called on a video node.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>