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
diff --git a/releases/voltha-2.4 b/releases/voltha-2.4
index b95718b..fdc27c0 100644
--- a/releases/voltha-2.4
+++ b/releases/voltha-2.4
@@ -3,9 +3,9 @@
 #
 # Source this file before running ./voltha up to install the VOLTHA 2.4.0 release
 
-export VOLTHA_CHART_VERSION=2.5.6
+export VOLTHA_CHART_VERSION=2.5.7
 export VOLTHA_BBSIM_CHART_VERSION=3.1.0
-export VOLTHA_ADAPTER_OPEN_OLT_CHART_VERSION=2.5.8
+export VOLTHA_ADAPTER_OPEN_OLT_CHART_VERSION=2.5.9
 export VOLTHA_ADAPTER_OPEN_ONU_CHART_VERSION=2.4.6
 export ONOS_CLASSIC_CHART_VERSION=0.1.1
 export RADIUS_CHART_VERSION=1.0.1