"vfs: fix d_path() for unreachable paths"

generally changed d_path() to report unreachable paths with a special
prefix.  This has an effect on /proc/${PID}/maps as well for memory maps
set up with shmem_file_setup() or hugetlb_file_setup().  These functions
set up unlinked files under a kernel-private vfsmount.  Since this
vfsmount is unreachable from userspace, these maps will be reported with
the "(unreachable)" prefix.

This is undesirable, because it changes the kernel ABI and might break
applications for no good reason.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Andreas Gruenbacher <agruen@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>