camera: Rename mBuf to mSlot

Bug: 19769719
Change-Id: I9eef512f2a2185b7e0298113d2503b62ec2e5942
diff --git a/services/camera/libcameraservice/gui/RingBufferConsumer.h b/services/camera/libcameraservice/gui/RingBufferConsumer.h
index 83e7298..243ea31 100644
--- a/services/camera/libcameraservice/gui/RingBufferConsumer.h
+++ b/services/camera/libcameraservice/gui/RingBufferConsumer.h
@@ -133,7 +133,7 @@
         }
 
         bool isEmpty() {
-            return mBufferItem.mBuf == BufferQueue::INVALID_BUFFER_SLOT;
+            return mBufferItem.mSlot == BufferQueue::INVALID_BUFFER_SLOT;
         }
 
         BufferItem& getBufferItem() { return mBufferItem; }