ALSA: control-led: use strscpy in set_led_id()

The use of strncpy() in the set_led_id() was incorrect.
The len variable should use 'min(sizeof(buf2) - 1, count)'
expression.

Use strscpy() function to simplify things and handle the error gracefully.

Fixes: a135dfb ("ALSA: led control - add sysfs kcontrol LED marking layer")
Reported-by: yang.yang29@zte.com.cn
Link: https://lore.kernel.org/alsa-devel/202301091945513559977@zte.com.cn/
Cc: <stable@vger.kernel.org>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/control_led.c

@@ -530,12 +530,11 @@ static ssize_t set_led_id(struct snd_ctl_led_card *led_card, const char *buf, si
 			  bool attach)
 {
 	char buf2[256], *s, *os;
-	size_t len = max(sizeof(s) - 1, count);
 	struct snd_ctl_elem_id id;
 	int err;
 
-	strncpy(buf2, buf, len);
-	buf2[len] = '\0';
+	if (strscpy(buf2, buf, sizeof(buf2)) < 0)
+		return -E2BIG;
 	memset(&id, 0, sizeof(id));
 	id.iface = SNDRV_CTL_ELEM_IFACE_MIXER;
 	s = buf2;