media: saa7134: Use video_unregister_device for radio_dev

The radio device doesn't use vb2, thus calling vb2_video_unregister_device()
which results in the following warning being printed on module unload.

WARNING: CPU: 1 PID: 215963 at drivers/media/common/videobuf2/videobuf2-v4l2.c:1236 vb2_video_unregister_device+0xc6/0xe0 [videobuf2_v4l2]

Fixes: 11788d9b ("media: media/pci: use vb2_video_unregister_device()")
Signed-off-by: Tasos Sahanidis <tasos@tasossah.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>