buffer_queue: Make reference parameter of SetPreallocatedBuffer const

This is simply copied by value, so there's no need to make it a
modifiable reference.

While we're at it, make the names of the parameters match its
definition.

src/core/hle/service/nvflinger/buffer_queue.cpp

@@ -16,7 +16,7 @@ BufferQueue::BufferQueue(u32 id, u64 layer_id) : id(id), layer_id(layer_id) {
         Kernel::Event::Create(Kernel::ResetType::Sticky, "BufferQueue NativeHandle");
 }
 
-void BufferQueue::SetPreallocatedBuffer(u32 slot, IGBPBuffer& igbp_buffer) {
+void BufferQueue::SetPreallocatedBuffer(u32 slot, const IGBPBuffer& igbp_buffer) {
     Buffer buffer{};
     buffer.slot = slot;
     buffer.igbp_buffer = igbp_buffer;

src/core/hle/service/nvflinger/buffer_queue.h

@@ -72,7 +72,7 @@ public:
         MathUtil::Rectangle<int> crop_rect;
     };
 
-    void SetPreallocatedBuffer(u32 slot, IGBPBuffer& buffer);
+    void SetPreallocatedBuffer(u32 slot, const IGBPBuffer& igbp_buffer);
     boost::optional<u32> DequeueBuffer(u32 width, u32 height);
     const IGBPBuffer& RequestBuffer(u32 slot) const;
     void QueueBuffer(u32 slot, BufferTransformFlags transform,