ftrace:test.d--00basic--basic2.tc fails on focal:linux-hwe-5.15 ppc64el when testing "function" tracer

Seen first time since the ftrace refactor.

Issue found on node PowerPC node gulpin with 5.15.0-79.86~20.04.2 in cycle sru-20230710.

Test crashed with the "function" tracer in tools/testing/selftests/ftrace/test.d/00basic/basic2.tc when testing available tracers

Test output:
 + [ 2 -eq 1 ]
 + [ -f set_event_pid ]
 + echo
 + [ -f set_ftrace_pid ]
 + echo
 + [ -f set_ftrace_notrace ]
 + echo
 + [ -f set_graph_function ]
 + [ -f stack_trace_filter ]
 + [ -f kprobe_events ]
 + [ -f uprobe_events ]
 + [ -f synthetic_events ]
 + [ -f snapshot ]
 + echo 0
 + clear_trace
 + echo
 + enable_tracing
 + echo 1
 + . /home/ubuntu/autotest/client/tmp/ubuntu_kselftests_ftrace/src/linux/tools/testing/selftests/ftrace/test.d/00basic/basic2.tc
 + test -f available_tracers
 + cat available_tracers
 + echo timerlat
 + echo osnoise
 + echo hwlat
 + echo wakeup_dl
 + echo wakeup_rt
 + echo wakeup
 + echo function
(Test interrupted here)

Note that this test has passed with 5.15.0-82.91~20.04.1 on node gulpin in cycle s2023.07.10