io_uring: kill extra wake_up_process in tw add

TWA_SIGNAL already wakes the thread, no need in wake_up_process() after
it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/7e90cf643f633e857443e0c9e72471b221735c50.1631115443.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>