perf evlist: Fix add() not propagating maps

If evsels are added after maps are created, then they won't have any
maps propagated to them.  Fix that.

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/1441699142-18905-12-git-send-email-adrian.hunter@intel.com
[ Moved the moving of propagate_maps() to the patch before, so that this
  one does _just_ the one lile fix calling in add()]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>