update setup_env shell script, fix set -e bug

guowenxue

2019-08-24 f8f05031c8278c8ad6dd18714c2a82d930dbfcbd

linux-bsp/tarballs/linux-at91.tar.xz does not exist in tree e0a9a48b914167544785dd245b1c9906e81b7fd8