fs: deduplicate noop_backing_dev_info

hugetlbfs, kernfs and dlmfs can simply use noop_backing_dev_info instead
of creating a local duplicate.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --cc fs/hugetlbfs/inode.c
Simple merge

diff --cc fs/kernfs/inode.c
Simple merge

diff --cc fs/kernfs/kernfs-internal.h
Simple merge

diff --cc fs/kernfs/mount.c
Simple merge

diff --cc fs/ocfs2/dlmfs/dlmfs.c
Simple merge