ALSA: pci: constify snd_kcontrol_new structures

Declare snd_kcontrol_new structures as const as they are only passed as
an argument to the function snd_ctl_new1. This argument is of type
const, so snd_kcontrol_new structures having the same property can be
made const too.
Done using Coccinelle:

@r1 disable optional_qualifier @
identifier i;
position p;
@@
static struct snd_kcontrol_new i@p = {...};

@ok1@
identifier r1.i;
position p;
expression e1;
@@
snd_ctl_new1(&i@p,e1)

@bad@
position p!={r1.p,ok1.p};
identifier r1.i;
@@
i@p

@depends on !bad disable optional_qualifier@
identifier r1.i;
@@
+const
struct snd_kcontrol_new i;

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/pci/lx6464es/lx6464es.c b/sound/pci/lx6464es/lx6464es.c
index c0f0c34..f9c3e86 100644
--- a/sound/pci/lx6464es/lx6464es.c
+++ b/sound/pci/lx6464es/lx6464es.c
@@ -899,7 +899,7 @@
 	return changed;
 }
 
-static struct snd_kcontrol_new lx_control_playback_switch = {
+static const struct snd_kcontrol_new lx_control_playback_switch = {
 	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
 	.name = "PCM Playback Switch",
 	.index = 0,