KVM: PPC: fix couple of memory leaks in MPIC/XICS devices

XICS failed to free xics structure on error path. MPIC destroy handler
forgot to delete kvm_device structure.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>