video_core: Add missing override specifiers

Ensures that the signatures will always match with the base class.

Also silences a few compilation warnings.

src/video_core/renderer_vulkan/vk_resource_manager.cpp

@@ -21,7 +21,7 @@ public:
     CommandBufferPool(const VKDevice& device)
         : VKFencedPool(COMMAND_BUFFER_POOL_SIZE), device{device} {}
 
-    void Allocate(std::size_t begin, std::size_t end) {
+    void Allocate(std::size_t begin, std::size_t end) override {
         const auto dev = device.GetLogical();
         const auto& dld = device.GetDispatchLoader();
         const u32 graphics_family = device.GetGraphicsFamily();

src/video_core/renderer_vulkan/vk_resource_manager.h

@@ -97,7 +97,7 @@ private:
 class VKFenceWatch final : public VKResource {
 public:
     explicit VKFenceWatch();
-    ~VKFenceWatch();
+    ~VKFenceWatch() override;
 
     /// Waits for the fence to be released.
     void Wait();