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>
Cc: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>