vulkan: Fix GetSpecific*ProcAddr for extension functions

Change-Id: Ib19e08b9e057affe348e0da5e6840e139d4ec292
(cherry picked from commit b7f5ef5d5fee72fc16fb3e883b0d1725f2c7feed)
diff --git a/vulkan/libvulkan/get_proc_addr.cpp b/vulkan/libvulkan/get_proc_addr.cpp
index 5247950..8aee40b 100644
--- a/vulkan/libvulkan/get_proc_addr.cpp
+++ b/vulkan/libvulkan/get_proc_addr.cpp
@@ -407,7 +407,7 @@
         return nullptr;
     const unsigned char* base = reinterpret_cast<const unsigned char*>(vtbl);
     return *reinterpret_cast<PFN_vkVoidFunction*>(
-        const_cast<unsigned char*>(base) + entry->offset);
+               const_cast<unsigned char*>(base) + offset);
 }
 
 PFN_vkVoidFunction GetSpecificDeviceProcAddr(const DeviceVtbl* vtbl,
@@ -436,7 +436,7 @@
         return nullptr;
     const unsigned char* base = reinterpret_cast<const unsigned char*>(vtbl);
     return *reinterpret_cast<PFN_vkVoidFunction*>(
-        const_cast<unsigned char*>(base) + entry->offset);
+               const_cast<unsigned char*>(base) + offset);
 }
 
 bool LoadInstanceVtbl(VkInstance instance,