TOMOYO: Fix pathname handling of disconnected paths.

Current tomoyo_realpath_from_path() implementation returns strange pathname
when calculating pathname of a file which belongs to lazy unmounted tree.
Use local pathname rather than strange absolute pathname in that case.

Also, this patch fixes a regression by commit 02125a82 "fix apparmor
dereferencing potentially freed dentry, sanitize __d_path() API".

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>