ALSA: gus: Fix kctl->id initialization

commit c5ae57b1 upstream.

GUS driver replaces the kctl->id.index after assigning the kctl via
snd_ctl_add().  This doesn't work any longer with the new Xarray
lookup change.  It has to be set before snd_ctl_add() call instead.

Fixes: c27e1efb

 ("ALSA: control: Use xarray for faster lookups")
Cc: <stable@vger.kernel.org>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230606093855.14685-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>