ALSA: atmel: Constify snd_ac97_bus_ops definitions

Now snd_ac97_bus() takes the const ops pointer, so we can define the
snd_ac97_bus_ops locally as const as well for further optimization.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-26-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/atmel/ac97c.c

@@ -702,7 +702,7 @@ static int atmel_ac97c_probe(struct platform_device *pdev)
 	struct atmel_ac97c		*chip;
 	struct resource			*regs;
 	struct clk			*pclk;
-	static struct snd_ac97_bus_ops	ops = {
+	static const struct snd_ac97_bus_ops	ops = {
 		.write	= atmel_ac97c_write,
 		.read	= atmel_ac97c_read,
 	};