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

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: e669e833da8d ("perf evsel: Restore evsel->priv as a tool private area")
Link: http://lkml.kernel.org/r/20171109150046.GN4333@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>