perf tools: Initialize reference counts in map__clone()

perf tools: Initialize reference counts in map__clone()

Map clone was written before we introduced reference counts for
maps and dsos, so all that was needed was just a copy and then we
would insert it into the new map_groups instance.

Fix it by, after copying, initializing the map->refcnt, grabbing
a struct dso refcount and resetting pointers that may be used
to determine if a map, when deleted, is in a rb_tree.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-pd4mr80o5b9gvk50iineacec@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>