perf stat: Fix cpu map index in bperf cgroup code

The previous cpu map introduced a bug in the bperf cgroup counter.  This
results in a failure when user gives a partial cpu map starting from
non-zero.

  $ sudo ./perf stat -C 1-2 --bpf-counters --for-each-cgroup ^. sleep 1
  libbpf: prog 'on_cgrp_switch': failed to create BPF link for perf_event FD 0:
                                 -9 (Bad file descriptor)
  Failed to attach cgroup program

To get the FD of an evsel, it should use a map index not the CPU number.

Fixes: 0255571 ("perf cpumap: Switch to using perf_cpu_map API")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: bpf@vger.kernel.org
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/r/20220916184132.1161506-3-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: namhyung

tools/perf/util/bpf_counter_cgroup.c

@@ -95,7 +95,7 @@ static int bperf_load_program(struct evlist *evlist)
 
 	perf_cpu_map__for_each_cpu(cpu, i, evlist->core.all_cpus) {
 		link = bpf_program__attach_perf_event(skel->progs.on_cgrp_switch,
-						      FD(cgrp_switch, cpu.cpu));
+						      FD(cgrp_switch, i));
 		if (IS_ERR(link)) {
 			pr_err("Failed to attach cgroup program\n");
 			err = PTR_ERR(link);
@@ -123,7 +123,7 @@ static int bperf_load_program(struct evlist *evlist)
 
 			map_fd = bpf_map__fd(skel->maps.events);
 			perf_cpu_map__for_each_cpu(cpu, j, evlist->core.all_cpus) {
-				int fd = FD(evsel, cpu.cpu);
+				int fd = FD(evsel, j);
 				__u32 idx = evsel->core.idx * total_cpus + cpu.cpu;
 
 				err = bpf_map_update_elem(map_fd, &idx, &fd,