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

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.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>