V4L/DVB (11059): xc5000: fix bug for hybrid xc5000 devices with IF other than 5380

The xc5000 driver has a bug where the IF is always set to whatever the first
caller to dvb_attach() provides.  This fails when the device requires an IF
other than 5380 and the analog driver is loaded first through tuner-core
(which always supplies the hard-coded value of 5380).

Thanks to Michael Krufky <mkrufky@linuxtv.org> and Steven Toth
<stoth@linuxtv.org> for providing sample hardware, engineering level support,
and testing.

Signed-off-by: Devin Heitmueller <dheitmueller@linuxtv.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>