perf hist: Correct hist_entry->mem_info refcounts

perf hist: Correct hist_entry->mem_info refcounts

The 'struct mem_info' is created by iter_prepare_mem_entry() at the
beginning and destroyed by iter_finish_mem_entry() at the end.

So if it's used in a new hist_entry, it should be cloned.

Simplify (hopefully) the logic by adding some helper functions and by
not holding the refcount in the temporary entry.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20240731235505.710436-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>