native: Rename mBuf to mSlot

Remove the union in BufferItem.

Bug: 19769719
Change-Id: I4e496b5aafce0fc5206dc7551a741f9c262c2cd0
diff --git a/services/surfaceflinger/SurfaceFlingerConsumer.cpp b/services/surfaceflinger/SurfaceFlingerConsumer.cpp
index ed1f31b..930e7c7 100644
--- a/services/surfaceflinger/SurfaceFlingerConsumer.cpp
+++ b/services/surfaceflinger/SurfaceFlingerConsumer.cpp
@@ -72,9 +72,9 @@
     // We call the rejecter here, in case the caller has a reason to
     // not accept this buffer.  This is used by SurfaceFlinger to
     // reject buffers which have the wrong size
-    int buf = item.mBuf;
-    if (rejecter && rejecter->reject(mSlots[buf].mGraphicBuffer, item)) {
-        releaseBufferLocked(buf, mSlots[buf].mGraphicBuffer, EGL_NO_SYNC_KHR);
+    int slot = item.mSlot;
+    if (rejecter && rejecter->reject(mSlots[slot].mGraphicBuffer, item)) {
+        releaseBufferLocked(slot, mSlots[slot].mGraphicBuffer, EGL_NO_SYNC_KHR);
         return BUFFER_REJECTED;
     }