vk_master_semaphore: Deduplicate atomic access within IsFree()

We can just reuse the already existing KnownGpuTick() to deduplicate the
access.

src/video_core/renderer_vulkan/vk_master_semaphore.h

@@ -36,7 +36,7 @@ public:
 
     /// Returns true when a tick has been hit by the GPU.
     [[nodiscard]] bool IsFree(u64 tick) const noexcept {
-        return gpu_tick.load(std::memory_order_relaxed) >= tick;
+        return KnownGpuTick() >= tick;
     }
 
     /// Advance to the logical tick.