ALSA: control: fix failure to return numerical ID in 'add' event

Currently when adding a new control, the assigned numerical ID is not
set for event data, thus userspace applications cannot realize it just
by event data.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>