platform/x86: asus-wmi: use brightness_set_blocking() for kbd led

kbd_led_set() can sleep, and so may not be used as the brightness_set()
callback.

Otherwise using this led with a trigger leads to system hangs
accompanied by:
BUG: scheduling while atomic: acpi_fakekeyd/2588/0x00000003
CPU: 4 UID: 0 PID: 2588 Comm: acpi_fakekeyd Not tainted 6.17.9+deb14-amd64 #1 PREEMPT(lazy)  Debian 6.17.9-1
Hardware name: ASUSTeK COMPUTER INC. ASUS EXPERTBOOK B9403CVAR/B9403CVAR, BIOS B9403CVAR.311 12/24/2024
Call Trace:
 <TASK>
 [...]
 schedule_timeout+0xbd/0x100
 __down_common+0x175/0x290
 down_timeout+0x67/0x70
 acpi_os_wait_semaphore+0x57/0x90
 [...]
 asus_wmi_evaluate_method3+0x87/0x190 [asus_wmi]
 led_trigger_event+0x3f/0x60
 [...]

Fixes: 9fe44fc ("platform/x86: asus-wmi: Simplify the keyboard brightness updating process")
Signed-off-by: Anton Khirnov <anton@khirnov.net>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Denis Benato <benato.denis96@gmail.com>
Link: https://patch.msgid.link/20251129101307.18085-3-anton@khirnov.net
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: elenril

drivers/platform/x86/asus-wmi.c

@@ -1704,14 +1704,14 @@ static void do_kbd_led_set(struct led_classdev *led_cdev, int value)
 	kbd_led_update(asus);
 }
 
-static void kbd_led_set(struct led_classdev *led_cdev,
-			enum led_brightness value)
+static int kbd_led_set(struct led_classdev *led_cdev, enum led_brightness value)
 {
 	/* Prevent disabling keyboard backlight on module unregister */
 	if (led_cdev->flags & LED_UNREGISTERING)
-		return;
+		return 0;
 
 	do_kbd_led_set(led_cdev, value);
+	return 0;
 }
 
 static void kbd_led_set_by_kbd(struct asus_wmi *asus, enum led_brightness value)
@@ -1887,7 +1887,7 @@ static int asus_wmi_led_init(struct asus_wmi *asus)
 		asus->kbd_led_wk = led_val;
 		asus->kbd_led.name = "asus::kbd_backlight";
 		asus->kbd_led.flags = LED_BRIGHT_HW_CHANGED;
-		asus->kbd_led.brightness_set = kbd_led_set;
+		asus->kbd_led.brightness_set_blocking = kbd_led_set;
 		asus->kbd_led.brightness_get = kbd_led_get;
 		asus->kbd_led.max_brightness = 3;