arm/xlnx-zynqmp: fix memory leak

fix CID 1311372.

Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Message-Id: <1436489490-236-4-git-send-email-arei.gonglei@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
