Fix a SurfaceFlinger bug.

The bug caused SurfaceFlinger to constantly trigger reallocation of buffers
that requested a fixed size.

Change-Id: Ic993a60e6474e36a344c8b48d541a0d08b8c4faf
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 194c295..833181b 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -380,6 +380,7 @@
             mReqWidth  = reqWidth;
             mReqHeight = reqHeight;
             mReqFormat = reqFormat;
+            mFixedSize = reqWidth && reqHeight;
 
             lcblk->reallocateAllExcept(index);
         }