[PATCH] ecryptfs: lower root result must be adirectory

- Currently after path_lookup succeed we dot't have any guarantie what
  it is DIR. This must be explicitly demanded.
- path_lookup can't return negative dentry, So inode check is useless.

Signed-off-by: Dmitriy Monakhov <dmonakhov@openvz.org>
Acked-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>