io_uring: mark the need to lock/unlock the ring as unlikely

Any of the fast paths will already have this locked, this helper only
exists to deal with io-wq invoking request issue where we do not have
the ctx->uring_lock held already. This means that any common or fast
path will already have this locked, mark it as such.

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