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

It maintains per-cpu pointers for the current thread but it doesn't
release the refcounts.

Fixes: 5e895278 ("perf sched: Move curr_thread initialization to perf_sched__map()")
Reviewed-by: Ian Rogers <irogers@google.com>
Tested-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250703014942.1369397-4-namhyung@kernel.org


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