Use -DUSE_ETHERCAT=TRUE in make-script instead

i.e.:

mkdir -p $eeros_build_dir
pushd $eeros_build_dir
cmake -DCMAKE_INSTALL_PREFIX=$install_dir \
      -DCMAKE_BUILD_TYPE=Release \
      -DUSE_ETHERCAT=TRUE \
      $eeros_source_dir
make
make install