shill: tighten up constness of PropertyStore

BUG=chromium-os:20543
TEST=unittest

Change-Id: Ifa86f82a883b3c3ec61ce10f8d82564b9a036b04
Reviewed-on: http://gerrit.chromium.org/gerrit/7901
Tested-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
diff --git a/ipconfig_dbus_adaptor.cc b/ipconfig_dbus_adaptor.cc
index 26858e6..226adec 100644
--- a/ipconfig_dbus_adaptor.cc
+++ b/ipconfig_dbus_adaptor.cc
@@ -69,7 +69,10 @@
 void IPConfigDBusAdaptor::SetProperty(const string &name,
                                       const ::DBus::Variant &value,
                                       ::DBus::Error &error) {
-  if (DBusAdaptor::DispatchOnType(ipconfig_->store(), name, value, &error)) {
+  if (DBusAdaptor::DispatchOnType(ipconfig_->mutable_store(),
+                                  name,
+                                  value,
+                                  &error)) {
     PropertyChanged(name, value);
   }
 }