KVM: x86/xen: Fix cleanup logic in emulation of Xen schedop poll hypercalls

In the Linux kernel, the following vulnerability has been resolved: KVM: x86/xen: Fix cleanup logic in emulation of Xen schedop poll hypercalls kvm_xen_schedop_poll does a kmalloc_array() when a VM polls the host for more than one event channel potr (nr_ports > 1). After the kmalloc_array(), the error paths need to go through the "out" label, but the call to kvm_read_guest_virt() does not. [Adjusted commit message. - Paolo]