ALSA: control - introduce snd_ctl_notify_one() helper

This helper is required for the following generic LED mute
patch. The helper also simplifies some other functions.

Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20210317172945.842280-2-perex@perex.cz


Signed-off-by: Takashi Iwai <tiwai@suse.de>