HID: hid-asus.c: Maps key 0x35 (display off) to KEY_SCREENLOCK

On Windows systems, ASUS laptops uses the "turn display off" key
(usually fn+f6) to turn both display and keyboard backlit off. On Linux
systems, this key has no effect at all since most desktop enviroments
don't deal with KEY_DISPLAY_OFF. By mapping it to KEY_SCREENLOCK
instead, would enable desktop environments to handle this key as a
screen lock intent from the user, out of the box.

Signed-off-by: Vinícius Angiolucci Reis <angiolucci@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>