ext4: Block writes to journal device

Ask block layer to not allow other writers to open block device used
for ext4 journal.

Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20231101174325.10596-7-jack@suse.cz


Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>