perf trace: Drop thread refcount in trace__event_handler()

perf trace: Drop thread refcount in trace__event_handler()

We must pair:

   thread = machine__findnew_thread();

with thread__put(thread). Fix it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: c4191e55b874 ("perf trace: Show comm and tid for tracepoint events")
Link: https://lkml.kernel.org/n/tip-dkxsb8cwg87rmkrzrbns1o4z@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>