io_uring: always go async for unsupported fadvise flags

No point in issuing -> return -EAGAIN -> go async, when it can be done upfront.

Signed-off-by: Dylan Yudaken <dylany@meta.com>
Link: https://lore.kernel.org/r/20230127135227.3646353-4-dylany@meta.com


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