io_uring: always clear LINK_TIMEOUT after cancel

Move REQ_F_LINK_TIMEOUT clearing out of __io_kill_linked_timeout()
because it might return early and leave the flag set. It's not a
problem, but may be confusing.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>