PFW: Back synchronisation no longer fails

BZ: 80500

As forward synchronisation, back synchronisation no longer return false if
a syncer fails to backsynchronise.

On subsystem restart, it will be resynchronise, so the back
synchronisation failure is a warning not an error.

As a result this patch also prevents PFW initialisation failure in case
of unavailable subsystem.

Change-Id: I21fe05747153a63cb77ed784532f3cbbf184d820
Signed-off-by: Kevin Rocard <kevinx.rocard@intel.com>
Reviewed-on: http://android.intel.com:8080/87779
Reviewed-by: De Chivre, Renaud <renaud.de.chivre@intel.com>
Tested-by: Dixon, CharlesX <charlesx.dixon@intel.com>
Reviewed-by: Benavoli, Patrick <patrick.benavoli@intel.com>
Reviewed-by: cactus <cactus@intel.com>
Tested-by: cactus <cactus@intel.com>
diff --git a/parameter/HardwareBackSynchronizer.h b/parameter/HardwareBackSynchronizer.h
index 2f0d503..094da14 100644
--- a/parameter/HardwareBackSynchronizer.h
+++ b/parameter/HardwareBackSynchronizer.h
@@ -33,7 +33,7 @@
     CHardwareBackSynchronizer(const CConfigurableElement* pConfigurableElement, CParameterBlackboard* pParameterBlackboard);
 
     // Back synchronization
-    virtual bool sync();
+    virtual void sync();
 
 private:
     // Back syncer set