aio: Fix incorrect usage of eventfd_signal_allowed()

We should defer eventfd_signal() to the workqueue when
eventfd_signal_allowed() return false rather than return
true.

Fixes: b542e383 ("eventfd: Make signal recursion protection a task bit")
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Link: https://lore.kernel.org/r/20210913111928.98-1-xieyongji@bytedance.com


Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>