[media] MAINTAINERS: fix drivers/media/usb/dvb-usb/cxusb*

This driver was never at dvb-usb-v2, as far as I could see.

Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>