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

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: a135dfb5de15 ("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>