Backends: Vulkan: Fix building with VK_NO_PROTOTYPES. (#914, #5738).

Amend a588f00

backends/imgui_impl_vulkan.cpp

diff --git a/backends/imgui_impl_vulkan.cpp b/backends/imgui_impl_vulkan.cpp
index 16932e3..bedf3cf 100644
--- a/backends/imgui_impl_vulkan.cpp
+++ b/backends/imgui_impl_vulkan.cpp
@@ -191,6 +191,7 @@
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkDeviceWaitIdle) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkFlushMappedMemoryRanges) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkFreeCommandBuffers) \
+    IMGUI_VULKAN_FUNC_MAP_MACRO(vkFreeDescriptorSets) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkFreeMemory) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkGetBufferMemoryRequirements) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkGetImageMemoryRequirements) \