xen: free domain's vcpu array

This was overlooked in fb442e2171 ("x86_64: allow more vCPU-s per
guest").

This is XSA-149.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Ian Campbell <ian.campbell@citrix.com>

Index: xen-4.5.2-testing/xen/common/domain.c
===================================================================
--- xen-4.5.2-testing.orig/xen/common/domain.c
+++ xen-4.5.2-testing/xen/common/domain.c
@@ -406,6 +406,7 @@ struct domain *domain_create(
     if ( init_status & INIT_xsm )
         xsm_free_security_domain(d);
     free_cpumask_var(d->domain_dirty_cpumask);
+    xfree(d->vcpu);
     free_domain_struct(d);
     return ERR_PTR(err);
 }