perf record: Fix synthesis failure warnings

Some calls to synthesis functions set err < 0 but only warn about the
failure and continue.  However they do not set err back to zero, relying
on subsequent code to do that.

That changed with the introduction of option --synth. When --synth=no
subsequent functions that set err back to zero are not called.

Fix by setting err = 0 in those cases.

Example:

 Before:

   $ perf record --no-bpf-event --synth=all -o /tmp/huh uname
   Couldn't synthesize bpf events.
   Linux
   [ perf record: Woken up 1 times to write data ]
   [ perf record: Captured and wrote 0.014 MB /tmp/huh (7 samples) ]
   $ perf record --no-bpf-event --synth=no -o /tmp/huh uname
   Couldn't synthesize bpf events.

 After:

   $ perf record --no-bpf-event --synth=no -o /tmp/huh uname
   Couldn't synthesize bpf events.
   Linux
   [ perf record: Woken up 1 times to write data ]
   [ perf record: Captured and wrote 0.014 MB /tmp/huh (7 samples) ]

Fixes: 41b740b6 ("perf record: Add --synth option")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220907162458.72817-1-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -1906,14 +1906,18 @@ static int record__synthesize(struct record *rec, bool tail)
 
 	err = perf_event__synthesize_bpf_events(session, process_synthesized_event,
 						machine, opts);
-	if (err < 0)
+	if (err < 0) {
 		pr_warning("Couldn't synthesize bpf events.\n");
+		err = 0;
+	}
 
 	if (rec->opts.synth & PERF_SYNTH_CGROUP) {
 		err = perf_event__synthesize_cgroups(tool, process_synthesized_event,
 						     machine);
-		if (err < 0)
+		if (err < 0) {
 			pr_warning("Couldn't synthesize cgroup events.\n");
+			err = 0;
+		}
 	}
 
 	if (rec->opts.nr_threads_synthesize > 1) {