KVM: PPC: e500: Eliminate preempt_disable in local_sid_destroy_all

The only place it makes sense to call this function already needs
to have preemption disabled.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>