threading: avoid invalid GIPA call in vkCreateDevice

Save VkInstance in layer_data so that we query vkCreateDevice with a valid
instance.
diff --git a/layers/threading.cpp b/layers/threading.cpp
index c97722e..2de0052 100644
--- a/layers/threading.cpp
+++ b/layers/threading.cpp
@@ -65,6 +65,7 @@
         return result;
 
     layer_data *my_data = get_my_data_ptr(get_dispatch_key(*pInstance), layer_data_map);
+    my_data->instance = *pInstance;
     my_data->instance_dispatch_table = new VkLayerInstanceDispatchTable;
     layer_init_instance_dispatch_table(*pInstance, my_data->instance_dispatch_table, fpGetInstanceProcAddr);
 
@@ -120,12 +121,13 @@
 
 VKAPI_ATTR VkResult VKAPI_CALL CreateDevice(VkPhysicalDevice gpu, const VkDeviceCreateInfo *pCreateInfo,
                                             const VkAllocationCallbacks *pAllocator, VkDevice *pDevice) {
+    layer_data *my_instance_data = get_my_data_ptr(get_dispatch_key(gpu), layer_data_map);
     VkLayerDeviceCreateInfo *chain_info = get_chain_info(pCreateInfo, VK_LAYER_LINK_INFO);
 
     assert(chain_info->u.pLayerInfo);
     PFN_vkGetInstanceProcAddr fpGetInstanceProcAddr = chain_info->u.pLayerInfo->pfnNextGetInstanceProcAddr;
     PFN_vkGetDeviceProcAddr fpGetDeviceProcAddr = chain_info->u.pLayerInfo->pfnNextGetDeviceProcAddr;
-    PFN_vkCreateDevice fpCreateDevice = (PFN_vkCreateDevice)fpGetInstanceProcAddr(NULL, "vkCreateDevice");
+    PFN_vkCreateDevice fpCreateDevice = (PFN_vkCreateDevice)fpGetInstanceProcAddr(my_instance_data->instance, "vkCreateDevice");
     if (fpCreateDevice == NULL) {
         return VK_ERROR_INITIALIZATION_FAILED;
     }
@@ -138,7 +140,6 @@
         return result;
     }
 
-    layer_data *my_instance_data = get_my_data_ptr(get_dispatch_key(gpu), layer_data_map);
     layer_data *my_device_data = get_my_data_ptr(get_dispatch_key(*pDevice), layer_data_map);
 
     // Setup device dispatch table
diff --git a/layers/threading.h b/layers/threading.h
index 8e90f0a..c3db346 100644
--- a/layers/threading.h
+++ b/layers/threading.h
@@ -189,6 +189,8 @@
 };
 
 struct layer_data {
+    VkInstance instance;
+
     debug_report_data *report_data;
     std::vector<VkDebugReportCallbackEXT> logging_callback;
     VkLayerDispatchTable *device_dispatch_table;