ctl: improve comments for handling element data
ctl: improve comments for handling element data

Some parts of control API documentation are described with core-developer
friendly explanations. To usual developer such as me, they're quite hard
to understand.

This commit improves such comments for a part of APIs to handle data of
each element.

Signed-off-by: Takashi Sakamoto <d5ec7d0cd8074757a1f5eb708bc105c3065a65ea@sakamocchi.jp>
Signed-off-by: Takashi Iwai <4596b3305151c7ee743192a95d394341e3d3b644@suse.de>

tiwai/alsa-lib,alsa-project/alsa-lib,zedongchen/alsa-lib,alsa-project/alsa-lib,alsa-project/alsa-lib,alsa-project/alsa-lib,takaswie/alsa-lib,takaswie/alsa-lib,tiwai/alsa-lib,zedongchen/alsa-lib,takaswie/alsa-lib,tiwai/alsa-lib,zedongchen/alsa-lib,zedongchen/alsa-lib,takaswie/alsa-lib,zedongchen/alsa-lib,takaswie/alsa-lib,tiwai/alsa-lib