cmake: fix 2 typos in MSCG build

      CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR> -DCMAKE_POSITION_INDEPENDENT_CODE=${CMAKE_POSITION_INDEPENDENT_CODE} ${EXTRA_MSCG_OPTS}

      )

    ExternalProject_get_property(mscg_build INSTALL_DIR)

    set(MSCG_LIBRARIES ${INSTALL_DIR}/${CMAKE_INSTALL_LIBDIR}/libmxcg.a)

    set(MSCG_INCLUDE_DIRS ${INSTALL_DIR}/include)

    set(MSCG_LIBRARIES ${INSTALL_DIR}/${CMAKE_INSTALL_LIBDIR}/libmscg.a)

    set(MSCG_INCLUDE_DIRS ${INSTALL_DIR}/include/mscg)

    list(APPEND LAMMPS_DEPS mscg_build)

    if(NOT LAPACK_FOUND)

      add_dependencies(mscg_build linalg)