drbd: pass drbd_peer_device to __req_mod

In preparation to support multiple connections, we need to know which
one we need to modify the request state for.

Originally-from: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Link: https://lore.kernel.org/r/20230330102744.2128122-2-christoph.boehmwalder@linbit.com


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