HID: input: add mapping for Assistant key

According to HUTRR89 usage 0x1cb from the consumer page was assigned to
allow launching desktop-aware assistant application, so let's add the
mapping.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>