It is not really closing the cgroup, but instead dropping a reference
count and if it hits zero, then calling delete, which will, among other
cleanup shores, close the cgroup fd.

So it is really dropping a reference to that cgroup, and the method name
for that is "put", so rename close_cgroup() to cgroup__put() to follow
this naming convention.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-sccxpnd7bgwc1llgokt6fcey@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>