profiling: Add missing error return to script.

Change-Id: I73bc562773211a7f80fdfa918b14f28c482b30f1
diff --git a/tools/heap_profile b/tools/heap_profile
index 64999d1..5744477 100755
--- a/tools/heap_profile
+++ b/tools/heap_profile
@@ -151,6 +151,7 @@
       platform = 'mac'
     else:
       print("Invalid platform: {}".format(sys.platform), file=sys.stderr)
+      return 1
 
     trace_to_text_binary = load_trace_to_text(platform)