alsa-lib: ctl: improve documentation for identifier of control element

[GitHub pull_request - opened]

alsa-project/alsa-lib pull request #66 was opened from takaswie:

In documentation, there are two ways relevant to the identifier of control
element. However, the case of combination has the lack of parameters.

This commit improves documentation in this point.

Fixes: f3c24de8c0df ("ctl: add an overview for design of ALSA control interface")
Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>

Request URL   : https://github.com/alsa-project/alsa-lib/pull/66
Patch URL     : https://github.com/alsa-project/alsa-lib/pull/66.patch
Repository URL: https://github.com/alsa-project/alsa-lib