fix release build vulkan

src/gpu/vk/GrVkGpu.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrVkGpu.h"
 
 #include "GrContextOptions.h"
@@ skipping 339 matching lines @@
 #endif
 }
 
 GrVkGpu::~GrVkGpu() {
     shaderc_compiler_release(fCompiler);
     fCurrentCmdBuffer->end(this);
     fCurrentCmdBuffer->unref(this);
 
     // wait for all commands to finish
     fResourceProvider.checkCommandBuffers();
-    VkResult res = VK_CALL(QueueWaitIdle(fQueue));
+    SkDEBUGCODE(VkResult res =) VK_CALL(QueueWaitIdle(fQueue));
     // VK_ERROR_DEVICE_LOST is acceptable when tearing down (see 4.2.4 in spec)
     SkASSERT(VK_SUCCESS == res || VK_ERROR_DEVICE_LOST == res);
  
     // must call this just before we destroy the VkDevice
     fResourceProvider.destroyResources();
 
 #ifdef SK_DEBUG
     VK_CALL(DestroyDebugReportCallbackEXT(fVkInstance, fCallback, nullptr));
 #endif
 
@@ skipping 1292 matching lines @@
     int set_a_break_pt_here = 9;
     aglSwapBuffers(aglGetCurrentContext());
 #elif defined(SK_BUILD_FOR_WIN32)
     SwapBuf();
     int set_a_break_pt_here = 9;
     SwapBuf();
 #endif
 #endif
 }