ALSA: hda - Fix gcc compile warning

It's false positive, but annoying.
  sound/pci/hda/hda_codec.c: In function ‘get_empty_pcm_device’:
  sound/pci/hda/hda_codec.c:2772: warning: ‘dev’ may be used uninitialized in this function

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