io_uring: arm poll for non-nowait files

Don't check if we can do nowait before arming apoll, there are several
reasons for that. First, we don't care much about files that don't
support nowait. Second, it may be useful -- we don't want to be taking
away extra workers from io-wq when it can go in some async. Even if it
will go through io-wq eventually, it make difference in the numbers of
workers actually used. And the last one, it's needed to clean nowait in
future commits.

[kernel test robot: fix unused-var]

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/9d06f3cb2c8b686d970269a87986f154edb83043.1634425438.git.asml.silence@gmail.com


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