/usr/mips-linux-gnu/lib/libatomic.so.1 is in libatomic1-mips-cross 8-20180414-1ubuntu2cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/mips-linux-gnu/lib/libatomic.so.1.2.0
/usr/mips-linux-gnu/lib/libatomic.so.1.2.0