perf list: Fix JSON segfault by setting the used skip_duplicate_pmus callback

Json output didn't set the skip_duplicate_pmus callback yielding a
segfault.

Fixes: cd4e1ef ("perf pmus: Skip duplicate PMUs and don't print list suffix by default")
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@arm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20231129213428.2227448-2-irogers@google.com
[namhyung: updated subject line according to Arnaldo]
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Author: captain5050

tools/perf/builtin-list.c

@@ -434,6 +434,11 @@ static void json_print_metric(void *ps __maybe_unused, const char *group,
 	strbuf_release(&buf);
 }
 
+static bool json_skip_duplicate_pmus(void *ps __maybe_unused)
+{
+	return false;
+}
+
 static bool default_skip_duplicate_pmus(void *ps)
 {
 	struct print_state *print_state = ps;
@@ -503,6 +508,7 @@ int cmd_list(int argc, const char **argv)
 			.print_end = json_print_end,
 			.print_event = json_print_event,
 			.print_metric = json_print_metric,
+			.skip_duplicate_pmus = json_skip_duplicate_pmus,
 		};
 		ps = &json_ps;
 	} else {