perf evsel: Fix up leftover perf_evsel_stat usage via evsel->priv

I forgot one conversion, which got noticed by Thomas when running:

  $ perf stat  -e '{cpu-clock,instructions}' kill
  kill: not enough arguments
  Segmentation fault (core dumped)
  $

Fix it, those stats are in evsel->stats, not anymore in evsel->priv.
Reported-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Tested-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: e669e833 ("perf evsel: Restore evsel->priv as a tool private area")
Link: http://lkml.kernel.org/r/20171109150046.GN4333@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -1375,7 +1375,7 @@ perf_evsel__process_group_data(struct perf_evsel *leader,
 static int
 perf_evsel__read_group(struct perf_evsel *leader, int cpu, int thread)
 {
-	struct perf_stat_evsel *ps = leader->priv;
+	struct perf_stat_evsel *ps = leader->stats;
 	u64 read_format = leader->attr.read_format;
 	int size = perf_evsel__read_size(leader);
 	u64 *data = ps->group_data;