perf map: Check if the map still has some refcounts on exit

perf map: Check if the map still has some refcounts on exit

We were checking just if it was still on some rb tree, but that is not
the only way that this map can still have references, map->refcnt is
there exactly for this, use it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-hany65tbeavsax7n3xvwl9pc@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>