ALSA: hda: make snd_hdac_stream_clear() static

ALSA: hda: make snd_hdac_stream_clear() static

This helper has no users outside of hdac_stream.c. External users
should only use snd_hdac_stream_start() and snd_hdac_stream_stop().

No functional change beyond making the function static and removing
the symbol export.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20220919121041.43463-2-pierre-louis.bossart@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>