[ALSA] hda-intel - Fix detection of audio codec on Toshiba A100

Some boards have the audio codec on slot #3 while the modem codec
on slot #0.  The driver should continue to probe the slots when
no audio codec is found.
This fixes the problem of no device on Toshiba A100 (and some other
ATI SB450 devices).

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>