LU-1994 llite: don't release nd->path in ll_follow_link

LU-1994 llite: don't release nd->path in ll_follow_link

For 3.6 kernel, .follow_link is not allowed to release nd,
as VFS handles itself on error path. So we change to not do
it and report error via nd_set_link().

For all kernels, if ll_follow_link returns NULL and set
error via nd_set_link, VFS will release nd->path in
__vfs_follow_link(). This also matches most in-kernel fs
behavior.

Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: yang sheng <yang.sheng@intel.com>
Change-Id: I13b7e00822b983c47183ee38357e4490bea3c52c
Reviewed-on: http://review.whamcloud.com/4487
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>