Using the latest available charts for voltha-2.4

Change-Id: I630ddd2086d750b8b36014ef8574d3f880fea7ed
diff --git a/VERSION b/VERSION
index 220d8e0..24fadfe 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-5.1.5
+5.1.6-dev