SurfaceTexture: fix a verbose-log compile error

Change-Id: I045231207e068d950bb0cb5085717af5d9454ed1
diff --git a/libs/gui/SurfaceTexture.cpp b/libs/gui/SurfaceTexture.cpp
index fcd287c..4772189 100644
--- a/libs/gui/SurfaceTexture.cpp
+++ b/libs/gui/SurfaceTexture.cpp
@@ -498,8 +498,8 @@
         eglDestroySyncKHR(dpy, fence);
     }
 
-    ST_LOGV("dequeueBuffer: returning slot=%d buf=%p flags=%#x", buf,
-            mSlots[buf].mGraphicBuffer->handle, returnFlags);
+    ST_LOGV("dequeueBuffer: returning slot=%d buf=%p flags=%#x", *outBuf,
+            mSlots[*outBuf].mGraphicBuffer->handle, returnFlags);
 
     return returnFlags;
 }