This avoids ambiguity of parameters:

error: ambiguous reference to positional arguments by number in a tuple variant; change this to a named argument
  --> block/src/qcow/mod.rs:48:48
   |
48 |     #[error("File larger than max of {}: {0}", MAX_QCOW_FILE_SIZE)]
   |                                                ^^^^^^^^^^^^^^^^^^

Signed-off-by: Rob Bradford <[email protected]>