ALSA: es1688: 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/es1688/es1688.c

@@ -321,7 +321,7 @@ static int snd_es968_pnp_resume(struct pnp_card_link *pcard)
 }
 #endif
 
-static struct pnp_card_device_id snd_es968_pnpids[] = {
+static const struct pnp_card_device_id snd_es968_pnpids[] = {
 	{ .id = "ESS0968", .devs = { { "@@@0968" }, } },
 	{ .id = "ESS0968", .devs = { { "ESS0968" }, } },
 	{ .id = "", } /* end */