Added missing ASSERT_NE.

Test was failing with segmentation fault (and crashing whole VTS) when
device was not available.

Change-Id: Id0f28d061dc5858fa00ef1bac5f7aa467d860864

neuralnetworks/1.2/vts/functional/CompilationCachingTests.cpp

@@ -86,6 +86,7 @@ class CompilationCachingTest : public NeuralnetworksHidlTest {
   protected:
     void SetUp() override {
         NeuralnetworksHidlTest::SetUp();
+        ASSERT_NE(device.get(), nullptr);
 
         // Create cache directory.
         char cacheDirTemp[] = "/data/local/tmp/TestCompilationCachingXXXXXX";