[d3d11] Fix frame latency based on buffer count

We need to ignore the front buffer here since we synchronize after
presentation.

src/d3d11/d3d11_swapchain.cpp

@@ -685,7 +685,7 @@ namespace dxvk {
     if (m_frameLatencyCap)
       maxFrameLatency = std::min(maxFrameLatency, m_frameLatencyCap);
 
-    maxFrameLatency = std::min(maxFrameLatency, m_desc.BufferCount + 1);
+    maxFrameLatency = std::min(maxFrameLatency, m_desc.BufferCount);
     return maxFrameLatency;
   }