Fix OpenBisFileSystem wrong buffer type (#909)

As the title say.

Ryujinx.HLE/HOS/Services/Fs/FileSystemProxy/FileSystemProxyHelper.cs

@@ -115,8 +115,8 @@ namespace Ryujinx.HLE.HOS.Services.Fs.FileSystemProxy
 
         public static Result ReadFsPath(out FsPath path, ServiceCtx context, int index = 0)
         {
-            long position = context.Request.SendBuff[index].Position;
-            long size     = context.Request.SendBuff[index].Size;
+            long position = context.Request.PtrBuff[index].Position;
+            long size     = context.Request.PtrBuff[index].Size;
 
             byte[] pathBytes = context.Memory.ReadBytes(position, size);