misc: Fix IVirtualMemoryManager.Fill ignoring value (#2775)

This fix IVirtualMemoryManager.Fill to actually use the provided fill
value instead of 0.

This have no implication at the moment as everything that use it pass 0
but it is needed for some upcoming kernel fixes.

Ryujinx.Memory/IVirtualMemoryManager.cs

@@ -68,7 +68,7 @@ namespace Ryujinx.Memory
 
                 using var writableRegion = GetWritableRegion(va + subOffset, copySize);
 
-                writableRegion.Memory.Span.Fill(0);
+                writableRegion.Memory.Span.Fill(value);
             }
         }