address_space_map is calling address_space_to_flatview but it can
be called outside the RCU lock.  The function itself is calling
rcu_read_lock/rcu_read_unlock, just in the wrong place, so the
fix is easy.
Reviewed-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>