V4L/DVB (11962): dvb: Fix broken link in get_dvb_firmware for nxt2004 (A180)

Due to a reorganisation of AVermedia's websites, get_dvb_firmware
no longer works for nxt2004. Fix it.

Signed-off-by: Jan Ceuleers <jan.ceuleers@computer.org>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>