perf trace: Fix leaks of 'struct thread' in fprintf_sys_enter()

I've found some leaks from 'perf trace -a'.

It seems there are more leaks but this is what I can find for now.

Fixes: 70351029 ("perf thread: Add support for reading the e_machine type for a thread")
Reviewed-by: Howard Chu <howardchu95@gmail.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250403054213.7021-1-namhyung@kernel.org


[ split from a larget patch ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>