namei: take put_link() into {lookup,mountpoint,do}_last()

rationale: we'll need to have terminate_walk() do put_link() on
everything, which will mean that in some cases ..._last() will do
put_link() anyway.  Easier to have them do it in all cases.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc fs/namei.c
Simple merge