iommu/vt-d: Downgrade the warning if enabling irq remapping fails

This triggers on a MacBook Pro.
See https://bugzilla.redhat.com/show_bug.cgi?id=948262 for
the problem report.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Joerg Roedel <joro@8bytes.org>

drivers/iommu/intel_irq_remapping.c

@@ -664,8 +664,7 @@ error:
 	 */
 
 	if (x2apic_present)
-		WARN(1, KERN_WARNING
-			"Failed to enable irq remapping.  You are vulnerable to irq-injection attacks.\n");
+		pr_warn("Failed to enable irq remapping.  You are vulnerable to irq-injection attacks.\n");
 
 	return -1;
 }