There are no users for snd_hdac_ext_bus_device_init() and
snd_hdac_ext_bus_device_exit().

While at it, remove hdac_to_hda_priv() too for the exact same reason.
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20220816111727.3218543-6-cezary.rojewski@intel.comSigned-off-by: Takashi Iwai <tiwai@suse.de>