io_uring: use nospec annotation for more indexes

There are still several places that using pre array_index_nospec()
indexes, fix them up.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b01ef5ee83f72ed35ad525912370b729f5d145f4.1649336342.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>