arm64: dts: mt8173: Fix mmsys node name

Node names are supposed to match the class of the device, mmsys is a
system controller (syscon) not a clock controller, so change the node
name accordingly.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Link: https://lore.kernel.org/r/20200401201736.2980433-4-enric.balletbo@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>