V4L/DVB (5513): Bt878: prevent probing wrong card entry

I got strange message when I did modprobe bt878:
bt878_probe: card id=[0x0],[ <NULL> ] has DVB functions.
The card_list array is terminated by sentinel entry.
But this list is traversed by:
for (i = 0, dvb_cards = card_list; i < ARRAY_SIZE(card_list);
     i++, dvb_cards++) {
...
}
in bt878_probe().
So this loop checks dummy sentinel entry, too.
This patch removes unnecessary sentinel entry.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>