perf env: Fix sibling_dies memory leak

ASan reports a memory leak in perf_env while running:

  # perf test "41: Session topology"

Caused by sibling_dies not being freed.

This patch adds the required free.

Fixes: acae8b36

 ("perf header: Add die information in CPU topology")
Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/2140d0b57656e4eb9021ca9772250c24c032924b.1626343282.git.rickyman7@gmail.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>