ALSA: hda - Treat zero connection as non-error

The zero-length connection list happens so often on Haswell HDMI, and
it results in warning messages like
    ALSA: hda_codec: invalid CONNECT_LIST verb 5[1]:0
at each time the codec resumes from the power-save, which is fairly
annoying.

Since this is no real error, make it shown only in the verbose debug
mode.

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