ALSA: ad1816a: 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/ad1816a/ad1816a.c

@@ -63,7 +63,7 @@ MODULE_PARM_DESC(enable, "Enable ad1816a based soundcard.");
 module_param_array(clockfreq, int, NULL, 0444);
 MODULE_PARM_DESC(clockfreq, "Clock frequency for ad1816a driver (default = 0).");
 
-static struct pnp_card_device_id snd_ad1816a_pnpids[] = {
+static const struct pnp_card_device_id snd_ad1816a_pnpids[] = {
 	/* Analog Devices AD1815 */
 	{ .id = "ADS7150", .devs = { { .id = "ADS7150" }, { .id = "ADS7151" } } },
 	/* Analog Device AD1816? */