Fix memory leak on error

hw/ppc/spapr.c: Fix memory leak on error, it was introduced in bc09e061
hw/acpi/memory_hotplug.c: Fix memory leak on error, it was introduced in 34f2af3d

Signed-off-by: Stefano Dong (董兴水) <opensource.dxs@aliyun.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>