message: rafs: fix a bug in set prefetch table size of empty filesysetem
  For empty RAFS v6 filesystem, it has incorrectly non-zero prefetch table
  size.
diff: @@ -698,7 +698,7 @@ impl Bootstrap {
  if let Some(mut pt) = prefetch_table {
  // Device slots are very close to extended super block.
  ext_sb.set_prefetch_table_offset(prefetch_table_offset);
  - ext_sb.set_prefetch_table_size(pt.len() as u32 * size_of::<u32>() as u32);
  + ext_sb.set_prefetch_table_size(prefetch_table_size);
  bootstrap_ctx
  .writer
  .seek_offset(prefetch_table_offset as u64)
  