iommu/vt-d: fix wrong return value of dmar_table_init()

If dmar_table_init() fails to detect DMAR table on the first call,
it will return wrong result on following calls because it always
sets dmar_table_initialized no matter if succeeds or fails to
detect DMAR table.
Signed-off-by: NJiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: NJoerg Roedel <joro@8bytes.org>

drivers/iommu/dmar.c

@@ -472,24 +472,23 @@ int __init dmar_table_init(void)
 	static int dmar_table_initialized;
 	int ret;
 
-	if (dmar_table_initialized)
-		return 0;
-
-	dmar_table_initialized = 1;
-
-	ret = parse_dmar_table();
-	if (ret) {
-		if (ret != -ENODEV)
-			pr_info("parse DMAR table failure.\n");
-		return ret;
-	}
+	if (dmar_table_initialized == 0) {
+		ret = parse_dmar_table();
+		if (ret < 0) {
+			if (ret != -ENODEV)
+				pr_info("parse DMAR table failure.\n");
+		} else  if (list_empty(&dmar_drhd_units)) {
+			pr_info("No DMAR devices found\n");
+			ret = -ENODEV;
+		}
 
-	if (list_empty(&dmar_drhd_units)) {
-		pr_info("No DMAR devices found\n");
-		return -ENODEV;
+		if (ret < 0)
+			dmar_table_initialized = ret;
+		else
+			dmar_table_initialized = 1;
 	}
 
-	return 0;
+	return dmar_table_initialized < 0 ? dmar_table_initialized : 0;
 }
 
 static void warn_invalid_dmar(u64 addr, const char *message)