[media] v4l2-dev.c: fix g_parm regression in determine_valid_ioctls()

The field current_norm does not have to be set for g_parm to be a valid
ioctl. Remove that check, but add a check whether this is a video node
instead as g_parm only makes sense for those nodes.

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