Make sure dmi_system_id tables are NULL terminated.

Fixes: 70365027 ("pinctrl: cherryview: Add a quirk to make Acer
Chromebook keyboard work again")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>