ALSA: sound/atmel/ac97c.c: Fix device index for pcm

chip->pdev->id is -1 by default. This is an invalid index resulting in
device file names like /dev/snd/pcmC0D-1p.

Signed-off-by: Alexander Stein <alexanders83@web.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>