perf map: Fix error return code in maps__clone()

Although 'err' has been initialized to -ENOMEM, but it will be reassigned
by the "err = unwind__prepare_access(...)" statement in the for loop. So
that, the value of 'err' is unknown when map__clone() failed.

Fixes: 6c50258 ("perf unwind: Call unwind__prepare_access for forked thread")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: zhen lei <thunder.leizhen@huawei.com>
Link: http://lore.kernel.org/lkml/20210415092744.3793-1-thunder.leizhen@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: Zhen Lei

tools/perf/util/map.c

@@ -840,15 +840,18 @@ int maps__fixup_overlappings(struct maps *maps, struct map *map, FILE *fp)
 int maps__clone(struct thread *thread, struct maps *parent)
 {
 	struct maps *maps = thread->maps;
-	int err = -ENOMEM;
+	int err;
 	struct map *map;
 
 	down_read(&parent->lock);
 
 	maps__for_each_entry(parent, map) {
 		struct map *new = map__clone(map);
-		if (new == NULL)
+
+		if (new == NULL) {
+			err = -ENOMEM;
 			goto out_unlock;
+		}
 
 		err = unwind__prepare_access(maps, new, NULL);
 		if (err)