ALSA: gus: constify pnp_card_device_id

pnp_card_device_id are not supposed to change at runtime. All functions
working with pnp_card_device_id provided by <linux/pnp.h> work with
const pnp_card_device_id. So mark the non-const structs as const.
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/gus/interwave.c

@@ -136,7 +136,7 @@ struct snd_interwave {
 static int isa_registered;
 static int pnp_registered;
 
-static struct pnp_card_device_id snd_interwave_pnpids[] = {
+static const struct pnp_card_device_id snd_interwave_pnpids[] = {
 #ifndef SNDRV_STB
 	/* Gravis UltraSound Plug & Play */
 	{ .id = "GRV0001", .devs = { { .id = "GRV0000" } } },