After some strace analyzing I have figured out that it is trying to open the /dev/bus/usb/{roothub}/{devide} nodes. Since then the download cable's node was read only it failed.
I have written the following udev rule to the /etc/udev/rules.d/51-lattice.rules file inspired by my AVR doper's rule:
SUBSYSTEM=="usb", ACTION=="add", ATTR{idVendor}=="1134", ATTR{idProduct}=="8001", MODE="0666"