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: 0dd5041 ("perf addr_location: Add init/exit/copy functions")
Signed-off-by: Ben Gainey <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Tested-by: Ian Rogers <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: bengaineyarm

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)