ALSA: line6: Constify snd_ratden definitions

The snd_ratden definitions used in line6 drivers are all read-only, so
they can be marked as const.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-51-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/line6/pod.c b/sound/usb/line6/pod.c
index ee4c9d22..cd44cb5 100644
--- a/sound/usb/line6/pod.c
+++ b/sound/usb/line6/pod.c
@@ -110,7 +110,7 @@ enum {
 	POD_BUSY_MIDISEND
 };
 
-static struct snd_ratden pod_ratden = {
+static const struct snd_ratden pod_ratden = {
 	.num_min = 78125,
 	.num_max = 78125,
 	.num_step = 1,
diff --git a/sound/usb/line6/podhd.c b/sound/usb/line6/podhd.c
index 27bf61c..d37db32 100644
--- a/sound/usb/line6/podhd.c
+++ b/sound/usb/line6/podhd.c
@@ -42,7 +42,7 @@ struct usb_line6_podhd {
 
 #define line6_to_podhd(x)	container_of(x, struct usb_line6_podhd, line6)
 
-static struct snd_ratden podhd_ratden = {
+static const struct snd_ratden podhd_ratden = {
 	.num_min = 48000,
 	.num_max = 48000,
 	.num_step = 1,
diff --git a/sound/usb/line6/toneport.c b/sound/usb/line6/toneport.c
index d0a555d..94dd5e7 100644
--- a/sound/usb/line6/toneport.c
+++ b/sound/usb/line6/toneport.c
@@ -63,7 +63,7 @@ static int toneport_send_cmd(struct usb_device *usbdev, int cmd1, int cmd2);
 
 #define TONEPORT_PCM_DELAY 1
 
-static struct snd_ratden toneport_ratden = {
+static const struct snd_ratden toneport_ratden = {
 	.num_min = 44100,
 	.num_max = 44100,
 	.num_step = 1,