[ALSA] hda-intel - Probe additional slots only if necessary

Probing the codec slots on ATI controller causes problems on some
devices like Acer laptops.  On these devices, reading from codec
slot 3 results in the communication failure with the codec chip.
Meanwhile, some laptops (e.g. Gateway) have the codec connection
only on slot 3, and probing this slot is mandatory for them.
The patch improves the probing robustness.  The additional slots
are now checked only when no codecs are found in the primary three
slots.

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