[OpenCL] Fixes CUDA specific test run on SYCL (#56)

The testBadParentValuesOnGPU should only be run on CUDA devices, as the
test checks for particular CUDA behaviour. We don't actually provide a
SYCL kernel for GatherTree and so it's not a problem that the tests
don't target SYCL.

tensorflow/contrib/seq2seq/python/kernel_tests/beam_search_ops_test.py

@@ -65,7 +65,9 @@ class GatherTreeTest(test.TestCase):
         _ = beams.eval()
 
   def testBadParentValuesOnGPU(self):
-    if not test.is_gpu_available():
+    # Only want to run this test on CUDA devices, as gather_tree is not
+    # registered for SYCL devices.
+    if not test.is_gpu_available(cuda_only=True):
       return
     # (max_time = 4, batch_size = 1, beams = 3)
     # bad parent in beam 1 time 1; appears as a negative index at time 0