perf cs-etm: Fix potential NULL pointer dereference found by the smatch

perf cs-etm: Fix potential NULL pointer dereference found by the smatch
tool

Based on the following report from Smatch, fix the potential NULL
pointer dereference check.

  tools/perf/util/cs-etm.c:2545
  cs_etm__process_auxtrace_info() error: we previously assumed
  'session->itrace_synth_opts' could be null (see line 2541)

  tools/perf/util/cs-etm.c
  2541         if (session->itrace_synth_opts && session->itrace_synth_opts->set) {
  2542                 etm->synth_opts = *session->itrace_synth_opts;
  2543         } else {
  2544                 itrace_synth_opts__set_default(&etm->synth_opts,
  2545                                 session->itrace_synth_opts->default_no_sample);
                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^
  2546                 etm->synth_opts.callchain = false;
  2547         }

'session->itrace_synth_opts' is impossible to be a NULL pointer in
cs_etm__process_auxtrace_info(), thus this patch removes the NULL
test for 'session->itrace_synth_opts'.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20190708143937.7722-5-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>