perf maps: Add for_each_entry()/_safe() iterators

To reduce boilerplate, provide a more compact form using an idiom
present in other trees of data structures.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-59gmq4kg1r68ou1wknyjl78x@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 807cbca..cfa3c9f 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -438,7 +438,7 @@ int perf_event__synthesize_modules(struct perf_tool *tool, perf_event__handler_t
 	else
 		event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
 
-	for (pos = maps__first(maps); pos; pos = map__next(pos)) {
+	maps__for_each_entry(maps, pos) {
 		size_t size;
 
 		if (!__map__is_kmodule(pos))