linux-phytec-fsl

drm/exynos: mixer: Constify platform_device_id

The platform_device_id is not modified by the driver and core uses it as
const.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>