message: rafs: set chunk_bits correctly for RafsV6InodeChunkHeader
  This fixes a reading data corruption caused by incorrect chunk_bits
  which is previously calculated with (32 - leading_zeros), e.g. in our
  case, chunk_size is 1<<20, (32 - leading_zeros) is 21 instead of 20.
diff: @@ -531,7 +531,7 @@ impl RafsV6InodeChunkHeader {
  /// Create a new instance of `RafsV6InodeChunkHeader`.
  pub fn new(chunk_size: u32) -> Self {
  debug_assert!(chunk_size.is_power_of_two());
  - let chunk_bits = 32 - chunk_size.leading_zeros() as u16;
  + let chunk_bits = chunk_size.trailing_zeros() as u16;
  debug_assert!(chunk_bits >= EROFS_BLOCK_BITS as u16);
  let chunk_bits = chunk_bits - EROFS_BLOCK_BITS as u16;
  debug_assert!(chunk_bits <= EROFS_CHUNK_FORMAT_SIZE_MASK);
  