ALSA: ac97: Constify static struct attribute_group

The only usage of ac97_adapter_attr_group is to put its address in an
array of pointers to const attribute_group structs. Make it const to
allow the compiler to put it in read-only memory.
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20210131001241.2278-2-rikard.falkeborn@gmail.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/ac97/bus.c

@@ -273,7 +273,7 @@ static struct attribute *ac97_controller_device_attrs[] = {
 	NULL
 };
 
-static struct attribute_group ac97_adapter_attr_group = {
+static const struct attribute_group ac97_adapter_attr_group = {
 	.name	= "ac97_operations",
 	.attrs	= ac97_controller_device_attrs,
 };