Fix map_groups__clone to put cloned map after inserting it to the
map_groups.

Refcnt debugger shows:
  ----
  ==== [0] ====
  Unreclaimed map: 0x2a27ee0
  Refcount +1 => 1 at
    ./perf(map_groups__clone+0x8d) [0x4bb7ed]
    ./perf(thread__fork+0xbe) [0x4c1f9e]
    ./perf(machine__process_fork_event+0x216) [0x4b79a6]
    ./perf(perf_event__synthesize_threads+0x38b) [0x48135b]
    ./perf(cmd_top+0xdc6) [0x43cb76]
    ./perf() [0x477223]
    ./perf(main+0x617) [0x422077]
    /lib64/libc.so.6(__libc_start_main+0xf0) [0x7ff806af8fe0]
    ./perf() [0x4221ed]
  Refcount +1 => 2 at
    ./perf(map_groups__clone+0x128) [0x4bb888]
    ./perf(thread__fork+0xbe) [0x4c1f9e]
    ./perf(machine__process_fork_event+0x216) [0x4b79a6]
    ./perf(perf_event__synthesize_threads+0x38b) [0x48135b]
    ./perf(cmd_top+0xdc6) [0x43cb76]
    ./perf() [0x477223]
    ./perf(main+0x617) [0x422077]
    /lib64/libc.so.6(__libc_start_main+0xf0) [0x7ff806af8fe0]
    ./perf() [0x4221ed]
  Refcount -1 => 1 at
    ./perf(map_groups__exit+0x87) [0x4ba757]
    ./perf(map_groups__put+0x68) [0x4ba9a8]
    ./perf(thread__put+0x8b) [0x4c1aeb]
    ./perf(machine__delete_threads+0x81) [0x4b48f1]
    ./perf(perf_session__delete+0x4f) [0x4be63f]
    ./perf(cmd_top+0x1094) [0x43ce44]
    ./perf() [0x477223]
    ./perf(main+0x617) [0x422077]
    /lib64/libc.so.6(__libc_start_main+0xf0) [0x7ff806af8fe0]
    ./perf() [0x4221ed]
  ----

This shows map_groups__clone get the map twice and put it when
map_groups__exit.
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20151209021120.10245.95388.stgit@localhost.localdomainSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>