iommu/amd: Fix error return code in irq_remapping_alloc()

Fix to return a negative error code from the alloc_irq_index() error
handling case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index bf5ec0c..2bcaca5 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -3886,6 +3886,7 @@
 	}
 	if (index < 0) {
 		pr_warn("Failed to allocate IRTE\n");
+		ret = index;
 		goto out_free_parent;
 	}