block: remove the GENHD_FL_HIDDEN check in blkdev_get_no_open

Hidden gendisks never hash the block device inode, so this can't happen.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211122130625.1136848-8-hch@lst.de


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