dt-bindings: Add vendor prefix for Kionix, Inc.

Kionix manufactured MEMs sensors. There are Kionix acceleromoter sensor
drivers which can be used with device tree.

Signed-off-by: Robert Yang <decatf@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>