Fix issue 2929440

Fixed regression introduced by change a54d7d3d7dd691334189aab20d23c65710092869 in audioflinger mixer thread:
When the output stream is suspended, the sleep time between two writes must match the actual duration
of one output stream buffer otherwise the playback rate is not respected.

Change-Id: Ic5bebe890290d1f44aeff9dd3c142d18e26fff2a
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 5520551..51881f0 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -664,6 +664,7 @@
         virtual void            deleteTrackName_l(int name) = 0;
         virtual uint32_t        activeSleepTimeUs() = 0;
         virtual uint32_t        idleSleepTimeUs() = 0;
+        virtual uint32_t        suspendSleepTimeUs() = 0;
 
     private:
 
@@ -724,6 +725,7 @@
         virtual     void        deleteTrackName_l(int name);
         virtual     uint32_t    activeSleepTimeUs();
         virtual     uint32_t    idleSleepTimeUs();
+        virtual     uint32_t    suspendSleepTimeUs();
 
         AudioMixer*                     mAudioMixer;
     };
@@ -744,6 +746,7 @@
         virtual     void        deleteTrackName_l(int name);
         virtual     uint32_t    activeSleepTimeUs();
         virtual     uint32_t    idleSleepTimeUs();
+        virtual     uint32_t    suspendSleepTimeUs();
 
     private:
         void applyVolume(uint16_t leftVol, uint16_t rightVol, bool ramp);