Camera2: mark testPreparePerformance as known failure

Not all devices can pass this new test

Bug: 17989532
Change-Id: I50eaf009bc4eabcb6decffcbc424effd164e6825
diff --git a/tests/expectations/knownfailures.txt b/tests/expectations/knownfailures.txt
index ecb7050..f65cf46 100644
--- a/tests/expectations/knownfailures.txt
+++ b/tests/expectations/knownfailures.txt
@@ -179,5 +179,12 @@
     "android.hardware.camera2.cts.ImageReaderTest#testAllOutputYUVResolutions"
   ],
   bug: 18689511
+},
+{
+  description: "The new prepare performance test is not yet passing on all devices",
+  names: [
+    "android.hardware.camera2.cts.SurfaceViewPreviewTest#testPreparePerformance"
+  ],
+  bug: 17989532
 }
 ]