ALSA: es1968: Constify snd_es1968_tea575x_gpios

The snd_es1968_tea575x_gpios table is referred as read-only, hence it
can be declared as const gracefully.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-56-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

sound/pci/es1968.c

@@ -2529,7 +2529,7 @@ struct snd_es1968_tea575x_gpio {
 	char *name;
 };
 
-static struct snd_es1968_tea575x_gpio snd_es1968_tea575x_gpios[] = {
+static const struct snd_es1968_tea575x_gpio snd_es1968_tea575x_gpios[] = {
 	{ .data = 6, .clk = 7, .wren = 8, .most = 9, .name = "SF64-PCE2" },
 	{ .data = 7, .clk = 8, .wren = 6, .most = 10, .name = "M56VAP" },
 };