io_uring: don't check unrelated req->open.how in accept request

Looks like a victim of too much copy/paste, we should not be looking
at req->open.how in accept. The point is to check CLOEXEC and error
out, which we don't invalid direct descriptors on exec. Hence any
attempt to get a direct descriptor with CLOEXEC is invalid.

No harm is done here, as req->open.how.flags overlaps with
req->accept.flags, but it's very confusing and might change if either of
those command structs are modified.

Fixes: aaa4db12 ("io_uring: accept directly into fixed file table")
Signed-off-by: Jens Axboe <axboe@kernel.dk>