A Linux Driver Module is already using the Chip Select 0. To use it, the overlay spidev_disabler.dts is needed.
It can be compiled with:
dtc spidev_disabler.dts -O dtb >spidev_disabler.dtbo
and can be loaded with
sudo dtoverlay -d . spidev_disabler
Now the LKM can be loaded and the module should work!
For more information, see this forum post