flamegraph: Fix event tree traversal with depth > 3

Previously, the script only took into account of 2 levels of event
trees. This makes it properly recurse to support deeper structure.

Signed-off-by: Daiki Ueno <dueno@redhat.com>

Author: ueno

scripts/flamegraph.py

@@ -159,7 +159,10 @@ def parse_span(self, parent, span):
 
     def parse_spans(self, parent, spans):
         for span in spans:
-            self.parse_span(parent, span)
+            children = span.get("spans", [])
+            node = self.parse_span(parent, span)
+            if len(children) > 0:
+                self.parse_spans(node, children)
 
     def run(self):
         spans = json.load(self.args.input)