When commit id 'da86c6c2' added support for diskPriv->encinfo in
qemuDomainSecretDiskPrepare a change to qemuDomainSecretDiskDestroy
to was missed. Although qemuDomainDiskPrivateDispose probably would
do the trick.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>