perf stat: Fix handling of unsupported cgroup events when using BPF counters

When --for-each-cgroup option is used, it fails when any of events is
not supported and exits immediately.  This is not how 'perf stat'
handles unsupported events.

Let's ignore the failure and proceed with others so that the output is
similar to when BPF counters are not used:

Before:

  $ sudo ./perf stat -a --bpf-counters -e L1-icache-loads,L1-dcache-loads --for-each-cgroup system.slice,user.slice sleep 1
  Failed to open first cgroup events
  $

After it shows output similat to when --bpf-counters isn't specified:

  $ sudo ./perf stat -a --bpf-counters -e L1-icache-loads,L1-dcache-loads --for-each-cgroup system.slice,user.slice sleep 1

   Performance counter stats for 'system wide':

     <not supported>      L1-icache-loads                  system.slice
          29,892,418      L1-dcache-loads                  system.slice
     <not supported>      L1-icache-loads                  user.slice
          52,497,220      L1-dcache-loads                  user.slice
  $

Fixes: 944138f0

 ("perf stat: Enable BPF counter with --for-each-cgroup")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/r/20230104064402.1551516-4-namhyung@kernel.org


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