correct rcu_unlock_domain()

correct rcu_unlock_domain()

Match rcu_lock_domain(), and remove the slightly misleading comment:
This isn't just the companion to rcu_lock_domain_by_id() (and that
latter function indeed also keeps the domain locked, not the domain
list).

No functional change, as rcu_read_{,un}lock() ignore their arguments
anyway.

Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>