perf sched: Fix memory leaks in 'perf sched latency'

The work_atoms should be freed after use.  Add free_work_atoms() to
make sure to release all.  It should use list_splice_init() when merging
atoms to prevent accessing invalid pointers.

Fixes: b1ffe8f3 ("perf sched: Finish latency => atom rename and misc cleanups")
Reviewed-by: Ian Rogers <irogers@google.com>
Tested-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250703014942.1369397-8-namhyung@kernel.org


Signed-off-by: Namhyung Kim <namhyung@kernel.org>