HID: asus: change mapping from KEY_WLAN to KEY_RFKILL

The input mapping code incorrectly maps the Airplane Mode button to
KEY_WLAN, which stands for WiFi toggle, but doesn't affect Bluetooth
(and other active radios) which is expected behavior for Airplane
Mode.

The fix replaces KEY_WLAN with the more appropriate KEY_RFKILL.

The declared usage code 0x88 corresponds to Airplane Mode button on
all keyboards handled by hid-asus (I2C netbook keyboards and USB
RoG series keyboards), so the fix doesn't introduce any
inconsistencies across different models.

Signed-off-by: Matjaz Hegedic <matjaz.hegedic@gmail.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>