perf tests: Fix software clock events test setting maps

The test titled "Test software clock events have valid period values"
was setting cpu/thread maps directly.  Make it use the proper function
perf_evlist__set_maps() especially now that it also propagates the maps.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Link: http://lkml.kernel.org/r/1441699142-18905-15-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>