audioflinger: use sp<> for track proxy

AudioTrack and AudioRecord shared memory proxy (Proxy class) is
RefBase so should not be refenced by raw pointer.

Change-Id: Ic63e31cef97503b8e262d5dafd8ce8f1d72d5eb8
diff --git a/services/audioflinger/Threads.cpp b/services/audioflinger/Threads.cpp
index e2932f1..c41ebf5 100644
--- a/services/audioflinger/Threads.cpp
+++ b/services/audioflinger/Threads.cpp
@@ -4150,7 +4150,7 @@
                 // read original volumes with volume control
                 float typeVolume = mStreamTypes[track->streamType()].volume;
                 float v = masterVolume * typeVolume;
-                AudioTrackServerProxy *proxy = track->mAudioTrackServerProxy;
+                sp<AudioTrackServerProxy> proxy = track->mAudioTrackServerProxy;
                 gain_minifloat_packed_t vlr = proxy->getVolumeLR();
                 vlf = float_from_gain(gain_minifloat_unpack_left(vlr));
                 vrf = float_from_gain(gain_minifloat_unpack_right(vlr));
@@ -4670,7 +4670,7 @@
     } else {
         float typeVolume = mStreamTypes[track->streamType()].volume;
         float v = mMasterVolume * typeVolume;
-        AudioTrackServerProxy *proxy = track->mAudioTrackServerProxy;
+        sp<AudioTrackServerProxy> proxy = track->mAudioTrackServerProxy;
         gain_minifloat_packed_t vlr = proxy->getVolumeLR();
         left = float_from_gain(gain_minifloat_unpack_left(vlr));
         if (left > GAIN_FLOAT_UNITY) {