io_uring: remove 'issue_flags' argument for io_req_set_rsrc_node()

All callers already hold the ring lock and hence are passing '0',
remove the argument and the conditional locking that it controlled.

Suggested-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>