bcache: remove the cache_dev_name field from struct cache

Just use the %pg format specifier to print the name directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Coly Li <colyli@suse.de>
Link: https://lore.kernel.org/r/20211020143812.6403-6-colyli@suse.de


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