iommu: smar: Fix return value check of create_irq()

ia64 returns a negative error code when allocation fails andx86
returns 0. Make it handle both.

Signed-off-by: Thomas Gleixner <[e-mail]>
Reviewed-by: Grant Likely <[e-mail]>
Cc: Tony Luck <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Fenghua Yu <[e-mail]>
Cc: [e-mail]
Acked-by: Joerg Roedel <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

drivers/iommu/dmar.c

···
 		return 0;
 
 	irq = create_irq();
-	if (!irq) {
+	if (irq <= 0) {
 		pr_err("IOMMU: no free vectors\n");
 		return -EINVAL;
 	}