io_uring: don't use TIF_NOTIFY_SIGNAL to test for availability of task_work

[ Upstream commit 6434ec01 ]

Use task_work_pending() as a better test for whether we have task_work
or not, TIF_NOTIFY_SIGNAL is only valid if the any of the task_work
items had been queued with TWA_SIGNAL as the notification mechanism.
Hence task_work_pending() is a more reliable check.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: 22537c9f ("io_uring: use the right type for work_llist empty check")
Signed-off-by: Sasha Levin <sashal@kernel.org>