perf evsel: Ensure reserved member of PERF_SAMPLE_CPU is zero in perf_event__synthesize_sample()

PERF_SAMPLE_CPU contains the cpu number in the first 4 bytes and the
second 4 bytes are reserved. Ensure the reserved bytes are zero in
perf_event__synthesize_sample().

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1516108492-21401-3-git-send-email-adrian.hunter@intel.com


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