V4L/DVB (6084): cx88-alsa: Eliminate snd_cx88_cards

The driver kepts a static global array of snd_card pointers for each card
probed, which was never used.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>