policy_hal: revert the logic for setting force flag

Keep the logic to be the same as default policy manager.
This is to address volume unexpected applied for in call
music delivery.

Change-Id: Id46fd45457015bf9432532ff7aba5f67b29b6206
diff --git a/policy_hal/AudioPolicyManager.cpp b/policy_hal/AudioPolicyManager.cpp
index 2dd6a3c..8b9d1d1 100644
--- a/policy_hal/AudioPolicyManager.cpp
+++ b/policy_hal/AudioPolicyManager.cpp
@@ -1094,7 +1094,7 @@
                         outputDesc->sharesHwModuleWith(desc) &&
                         (newDevices != desc->devices())) {
                         DeviceVector dev = getNewOutputDevices(mOutputs.valueFor(curOutput), false /*fromCache*/);
-                        bool force = prevDevices != dev;
+                        bool force = desc->devices() != dev;
                         uint32_t delayMs;
                         if (dev == prevDevices) {
                             delayMs = 0;