ALSA: drivers: Constify snd_kcontrol_new items

Most of snd_kcontrol_new definitions are read-only and passed as-is.
Let's declare them as const for further optimization.
Constify snd_kcontrol_new items

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-34-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c
index cef5b39..cec682a 100644
--- a/sound/drivers/dummy.c
+++ b/sound/drivers/dummy.c
@@ -849,7 +849,7 @@ static int snd_dummy_iobox_put(struct snd_kcontrol *kcontrol,
 	return changed;
 }
 
-static struct snd_kcontrol_new snd_dummy_controls[] = {
+static const struct snd_kcontrol_new snd_dummy_controls[] = {
 DUMMY_VOLUME("Master Volume", 0, MIXER_ADDR_MASTER),
 DUMMY_CAPSRC("Master Capture Switch", 0, MIXER_ADDR_MASTER),
 DUMMY_VOLUME("Synth Volume", 0, MIXER_ADDR_SYNTH),