platform/x86: asus-wmi: Consider device is absent when the read is ~0

AAEON PICO-TGU4 board doesn't have any LED but there are bogus LED
controls under /sys/class/leds:
$ ls /sys/class/leds
asus::kbd_backlight asus::lightbar  platform::micmute

The reason is that the ~0 read from asus_wmi_get_devstate() is treated
as a valid state, in truth it means the device is absent.

So filter out ~0 read to prevent bogus LED controls being created.
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20240308053255.224496-1-kai.heng.feng@canonical.comSigned-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

drivers/platform/x86/asus-wmi.c

@@ -481,7 +481,17 @@ static int asus_wmi_evaluate_method_agfn(const struct acpi_buffer args)
 
 static int asus_wmi_get_devstate(struct asus_wmi *asus, u32 dev_id, u32 *retval)
 {
-	return asus_wmi_evaluate_method(asus->dsts_id, dev_id, 0, retval);
+	int err;
+
+	err = asus_wmi_evaluate_method(asus->dsts_id, dev_id, 0, retval);
+
+	if (err)
+		return err;
+
+	if (*retval == ~0)
+		return -ENODEV;
+
+	return 0;
 }
 
 static int asus_wmi_set_devstate(u32 dev_id, u32 ctrl_param,