fix release build vulkan

src/gpu/vk/GrVkGpu.cpp

Index: src/gpu/vk/GrVkGpu.cpp
diff --git a/src/gpu/vk/GrVkGpu.cpp b/src/gpu/vk/GrVkGpu.cpp
index 0666f10f7e200cc421a77616cf43f575d1cb8bae..926e423b6e3016b13fa999b100520e0abcb398bf 100644
--- a/src/gpu/vk/GrVkGpu.cpp
+++ b/src/gpu/vk/GrVkGpu.cpp
@@ -357,7 +357,7 @@ GrVkGpu::~GrVkGpu() {
 
     // 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);