ARM: shmobile: kzm9g: Use of_machine_is_compatible()

The machine number is hardcoded to ~0 on DT-enabled machines, making
machine_is_*() always fail when support for more than one machine is
compiled into the kernel. Replace the machine_is_kzm9g() call with
of_machine_is_compatible("renesas,kzm9g").

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>