init: don't remove the /dev/ prefix from error messages

Remove the code that drops the /dev/ prefix from root_device_name, which
is only used for error messages when mounting the root device fails.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230531125535.676098-10-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>