[media] bttv: Use btv->has_radio rather then the card info when registering the tuner

bttv_init_card2() sets btv->has_audio to a *default* value from the tvcards
array and then may update it by reading a card specific eeprom or gpio
detection.

After bttv_init_card2(), bttv_init_tuner() gets called, and it should clearly
use the updated, dynamic has_radio value from btv->has_radio, rather then
the const value in the tvcards array.

This fixes the radio not working on my Hauppauge WinTV.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>