policy_hal: avoid VOIP_RX flag is removed for voip call

When offload output starts with FLAG_DIRECT, then setup a
voip call, VOIP_RX flag will be overwritten to FLAG_NONE.
This causes voip usecase isn't set for voip call.

Fix by adding VOIP_RX flag check to avoid settting 
FLAG_NONE for voip call.

Change-Id: Iee89d53d7529e6235b31903376b30e3a23657e3f
diff --git a/policy_hal/AudioPolicyManager.cpp b/policy_hal/AudioPolicyManager.cpp
index 8216fc8..d84ed16 100644
--- a/policy_hal/AudioPolicyManager.cpp
+++ b/policy_hal/AudioPolicyManager.cpp
@@ -1701,7 +1701,8 @@
         // prevent direct pcm for non-music stream blindly if direct pcm already in use
         // for other music stream concurrency is handled after checking direct ouput usage
         // and checking client
-        if (direct_pcm_already_in_use == true && stream != AUDIO_STREAM_MUSIC) {
+        if (direct_pcm_already_in_use == true && stream != AUDIO_STREAM_MUSIC &&
+            !(*flags & AUDIO_OUTPUT_FLAG_VOIP_RX)) {
             ALOGD("disabling offload for non music stream as direct pcm is already in use");
             *flags = (audio_output_flags_t)(AUDIO_OUTPUT_FLAG_NONE);
         }