perf db-export: Fix missing reference count get in call_path_from_sample()

The addr_location map and maps fields in the inner loop were missing
calls to map__get()/maps__get(). The subsequent addr_location__exit()
call in each loop puts the map/maps fields causing use-after-free
aborts.

This issue reproduces on at least arm64 and x86_64 with something
simple like `perf record -g ls` followed by `perf script -s script.py`
with the following script:

    perf_db_export_mode = True
    perf_db_export_calls = False
    perf_db_export_callchains = True

    def sample_table(*args):
        print(f'sample_table({args})')

    def call_path_table(*args):
        print(f'call_path_table({args}')

Committer testing:

This test, just introduced by Ian Rogers, now passes, not segfaulting
anymore:

  # perf test "perf script tests"
   95: perf script tests                                               : Ok
  #

Fixes: 0dd5041c ("perf addr_location: Add init/exit/copy functions")
Signed-off-by: Ben Gainey <ben.gainey@arm.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20231207140911.3240408-1-ben.gainey@arm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/db-export.c

@@ -253,8 +253,8 @@ static struct call_path *call_path_from_sample(struct db_export *dbe,
 		 */
 		addr_location__init(&al);
 		al.sym = node->ms.sym;
-		al.map = node->ms.map;
-		al.maps = thread__maps(thread);
+		al.map = map__get(node->ms.map);
+		al.maps = maps__get(thread__maps(thread));
 		al.addr = node->ip;
 
 		if (al.map && !al.sym)