dm clone: Fix typo in block_device format specifier

Use %pg for printing the block device name, instead of %pd.

Fixes: 385411ff ("dm: stop using bdevname")
Cc: stable@vger.kernel.org # v5.18+
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>