ARM: dts: exynos: Add compatible for s5m8767 clocks node on Itop Core

The bindings for s2mps11/s5m8767 clocks driver require a compatible for
clocks node.  Parent MFD sec-core driver will also use it when
instantiating children.

The compatible is not needed for proper working because device will be
anyway created by parent MFD device.  Add it for correctness.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>