perf tests attr: Fix stat sample_type setup

>From following commit:

  commit 4979d0c7 ("perf stat record: Add record command")

we started to assign PERF_SAMPLE_IDENTIFIER to sample_type.

Fixing the attr stat tests accordingly.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Richter <tmricht@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20170703145030.12903-14-jolsa@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>