ALSA: hda - Check codec errors in snd_hda_get_connections()

The codec read errors in snd_hda_get_connections() are ignored so far,
and it causes a problem like the bug in the commit
    9d30937a
    ALSA: hda_intel: more strict alc880_parse_auto_config dig_nid checking

Better to check errors in the function and returns a proper error code
rather than passing bogus NID values.

Signed-off-by: Takashi Iwai <tiwai@suse.de>