ubuntu_ltp_controllers:memcg_stat: test5: hierarchical_memory_limit is incorrect on s390x

[Stefan Bader]

On s390x nodes (zVM and LPAR) with hirsute:linux (5.11) on sru-20210927 test #5 fails with the following output (the numbers are different between zVM and LPAR but same pattern):

memcg_stat_test 5 TINFO: Test hierarchical_memory_limit with enabling hierarchical accounting
echo: write error: Device or resource busy
memcg_stat_test 5 TFAIL: echo 167936 > memory.limit_in_bytes failed unexpectedly
memcg_stat_test 5 TPASS: echo 438272 > subgroup/memory.limit_in_bytes passed as expected
memcg_stat_test 5 TFAIL: hierarchical_memory_limit is 438272, 167936 expected