ocfs2: Fix refcnt leak on ocfs2_fast_follow_link() error path

If ->follow_link handler returns an error, it should decrement
nd->path refcnt. But ocfs2_fast_follow_link() doesn't decrement.

This patch fixes the problem by using nd_set_link() style error handling
instead of playing with nd->path.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Joel Becker <joel.becker@oracle.com>