[media] radio-tea5764: embed struct video_device

This simplifies the code as it removes a memory allocation check.

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