Update CMakeLists.txt
Update CMakeLists.txt

- fix CMake to define ChibiOS default branch when the CHIBIOS_VERSION option isn't set at all
nanoframework/nf-interpreter,nanoframework/nf-interpreter,Eclo/nf-interpreter,Eclo/nf-interpreter,Eclo/nf-interpreter,nanoframework/nf-interpreter,nanoframework/nf-interpreter,Eclo/nf-interpreter