perf test: Fix perf_event_attr test failure

Fix inconsistent use of tabs and spaces error:

  # perf test 16 -v
  16: Setup struct perf_event_attr                          :
  --- start ---
  test child forked, pid 20224
    File "/usr/libexec/perf-core/tests/attr.py", line 119
      log.warning("expected %s=%s, got %s" % (t, self[t], other[t]))
                                                                 ^
  TabError: inconsistent use of tabs and spaces in indentation
  test child finished with -1
  ---- end ----
  Setup struct perf_event_attr: FAILED!
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20181122140456.16817-1-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>