drbd: Balance RCU calls in drbd_adm_dump_devices()

drbd: Balance RCU calls in drbd_adm_dump_devices()

Make drbd_adm_dump_devices() call rcu_read_lock() before
rcu_read_unlock() is called. This has been detected by the Clang
thread-safety analyzer.

Tested-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Fixes: a55bbd375d18 ("drbd: Backport the "status" command")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20260326214054.284593-1-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>