V4L/DVB (3506): Cinergy T2 dmx cleanup on disconnect

Detaching the device didn't clean up several device files in /dev/dvb,
after applying that patch all dvb devices disappeared as expected.

Signed-off-by: Markus Rechberger <mrechberger@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>