qemu: domain: Initialize proper element in qemuDomainPrepareStorageSourceBlockdev

We are preparing a certain disk source passed in as '@src' so the
individual functions should use that rather than disk->src which
corresponds to the top level element of the chain only.

Without this change TLS and persistent reservations would not work for
backing images of a chain when using -blockdev.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_domain.c

@@ -13462,10 +13462,10 @@ qemuDomainPrepareStorageSourceBlockdev(virDomainDiskDefPtr disk,
                                              src->nodeformat) < 0)
         return -1;
 
-    if (qemuDomainPrepareStorageSourcePR(disk->src, priv, src->nodestorage) < 0)
+    if (qemuDomainPrepareStorageSourcePR(src, priv, src->nodestorage) < 0)
         return -1;
 
-    if (qemuDomainPrepareStorageSourceTLS(disk->src, cfg, src->nodestorage,
+    if (qemuDomainPrepareStorageSourceTLS(src, cfg, src->nodestorage,
                                           priv->qemuCaps) < 0)
         return -1;