xen: fix error handling path if xen_allocate_irq_dynamic fails

It is possible that the call to xen_allocate_irq_dynamic() returns negative
number other than -1.
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/events.c

@@ -840,7 +840,7 @@ int bind_evtchn_to_irq(unsigned int evtchn)
 
 	if (irq == -1) {
 		irq = xen_allocate_irq_dynamic();
-		if (irq == -1)
+		if (irq < 0)
 			goto out;
 
 		irq_set_chip_and_handler_name(irq, &xen_dynamic_chip,
@@ -944,7 +944,7 @@ int bind_virq_to_irq(unsigned int virq, unsigned int cpu)
 
 	if (irq == -1) {
 		irq = xen_allocate_irq_dynamic();
-		if (irq == -1)
+		if (irq < 0)
 			goto out;
 
 		irq_set_chip_and_handler_name(irq, &xen_percpu_chip,