io_uring/rsrc: Simplify buffer cloning by locking both rings

The locking in the buffer cloning code is somewhat complex because it goes
back and forth between locking the source ring and the destination ring.

Make it easier to reason about by locking both rings at the same time.
To avoid ABBA deadlocks, lock the rings in ascending kernel address order,
just like in lock_two_nondirectories().

Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/r/20250115-uring-clone-refactor-v2-1-7289ba50776d@google.com


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