bcache_register(): don't bother with set_blocksize()

We are not using __bread() anymore and read_cache_page_gfp() doesn't
care about block size.  Moreover, we should *not* change block
size on a device that is currently held exclusive - filesystems
that use buffer cache expect the block numbers to be interpreted
in units set by filesystem.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christian Brauner <brauner@kernel.org>
ACKed-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

drivers/md/bcache/super.c

@@ -2554,10 +2554,6 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 	if (IS_ERR(bdev_file))
 		goto out_free_sb;
 
-	err = "failed to set blocksize";
-	if (set_blocksize(file_bdev(bdev_file), 4096))
-		goto out_blkdev_put;
-
 	err = read_super(sb, file_bdev(bdev_file), &sb_disk);
 	if (err)
 		goto out_blkdev_put;