ALSA: hda - Fix NULL dereference with CONFIG_SND_DYNAMIC_MINORS=n

Without the dynamic minor assignment, HDMI codec may have less PCM
instances than the number of pins, which eventually leads to Oops.

Reported-by: Stratos Karafotis <stratosk@semaphore.gr>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>