ALSA: control_led - fix the stack usage (control element ops)

It's a bad idea to allocate big structures on the stack.
Mark the variables as static and add a note for the locking.

Fixes: 22d8de62f1 ("ALSA: control - add generic LED trigger module as the new control layer")
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20210414105858.1937710-1-perex@perex.cz
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/control_led.c

@@ -94,11 +94,15 @@ static struct snd_ctl_led *snd_ctl_led_get_by_access(unsigned int access)
 	return &snd_ctl_leds[group];
 }
 
+/*
+ * A note for callers:
+ *   The two static variables info and value are protected using snd_ctl_led_mutex.
+ */
 static int snd_ctl_led_get(struct snd_ctl_led_ctl *lctl)
 {
+	static struct snd_ctl_elem_info info;
+	static struct snd_ctl_elem_value value;
 	struct snd_kcontrol *kctl = lctl->kctl;
-	struct snd_ctl_elem_info info;
-	struct snd_ctl_elem_value value;
 	unsigned int i;
 	int result;