ALSA: hda - Add / fix kernel doc comments

Give some readable comment in kernel doc style for each exported
function, as I promised in the previous meetings.  While we're at it,
fix the wrong comments, too.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/hda/hdac_stream.c b/sound/hda/hdac_stream.c
index 8981159..38990a7 100644
--- a/sound/hda/hdac_stream.c
+++ b/sound/hda/hdac_stream.c
@@ -426,7 +426,8 @@
 }
 EXPORT_SYMBOL_GPL(snd_hdac_stream_setup_periods);
 
-/* snd_hdac_stream_set_params - set stream parameters
+/**
+ * snd_hdac_stream_set_params - set stream parameters
  * @azx_dev: HD-audio core stream for which parameters are to be set
  * @format_val: format value parameter
  *