Replace some nullptrs with VK_NULL_HANDLE

src/gpu/vk/GrVkPipeline.cpp

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #include "GrVkPipeline.h"
 
 #include "GrGeometryProcessor.h"
@@ skipping 477 matching lines @@
     pipelineCreateInfo.pColorBlendState = &colorBlendInfo;
     pipelineCreateInfo.pDynamicState = &dynamicInfo;
     pipelineCreateInfo.layout = layout;
     pipelineCreateInfo.renderPass = renderPass.vkRenderPass();
     pipelineCreateInfo.subpass = 0;
     pipelineCreateInfo.basePipelineHandle = VK_NULL_HANDLE;
     pipelineCreateInfo.basePipelineIndex = -1;
 
     VkPipeline vkPipeline;
     VkResult err = GR_VK_CALL(gpu->vkInterface(), CreateGraphicsPipelines(gpu->device(),
-                                                                          nullptr, 1, 
+                                                                          VK_NULL_HANDLE, 1, 
                                                                           &pipelineCreateInfo, 
                                                                           nullptr, &vkPipeline));
     if (err) {
         return nullptr;
     }
 
     return new GrVkPipeline(vkPipeline);
 }
 
 void GrVkPipeline::freeGPUData(const GrVkGpu* gpu) const {
     GR_VK_CALL(gpu->vkInterface(), DestroyPipeline(gpu->device(), fPipeline, nullptr));
 }