Return fence from acquireBuffer

Change-Id: Iab22054c1dc4fd84affab3cc5bbdcd5a1e689666
diff --git a/libs/gui/BufferQueue.cpp b/libs/gui/BufferQueue.cpp
index a868537..23e3a4f 100644
--- a/libs/gui/BufferQueue.cpp
+++ b/libs/gui/BufferQueue.cpp
@@ -885,11 +885,13 @@
         buffer->mFrameNumber = mSlots[buf].mFrameNumber;
         buffer->mTimestamp = mSlots[buf].mTimestamp;
         buffer->mBuf = buf;
+        buffer->mFence = mSlots[buf].mFence;
         mSlots[buf].mAcquireCalled = true;
 
         mSlots[buf].mBufferState = BufferSlot::ACQUIRED;
         mQueue.erase(front);
         mDequeueCondition.broadcast();
+        mSlots[buf].mFence.clear();
 
         ATRACE_INT(mConsumerName.string(), mQueue.size());
     } else {