xen/irq: If we fail during msi_capability_init return proper error code.

There are three different modes: PV, HVM, and initial domain 0. In all
the cases we would return -1 for failure instead of a proper error code.
Fix this by propagating the error code from the generic IRQ code.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 503614f..212a5c8 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -432,7 +432,8 @@
 
 	irq = irq_alloc_desc_from(first, -1);
 
-	xen_irq_init(irq);
+	if (irq >= 0)
+		xen_irq_init(irq);
 
 	return irq;
 }
@@ -713,7 +714,7 @@
 	mutex_lock(&irq_mapping_update_lock);
 
 	irq = xen_allocate_irq_dynamic();
-	if (irq == -1)
+	if (irq < 0)
 		goto out;
 
 	irq_set_chip_and_handler_name(irq, &xen_pirq_chip, handle_edge_irq,
@@ -729,7 +730,7 @@
 error_irq:
 	mutex_unlock(&irq_mapping_update_lock);
 	xen_free_irq(irq);
-	return -1;
+	return ret;
 }
 #endif