dm: core: Fix uninitialized return value from dm_scan_fdt_node

If there are no nodes or if all nodes are disabled, this function would
return err without setting it first. Fix this by initializing err to
zero.

Fixes: 94f7afdf ("dm: core: Ignore disabled devices when binding")
Signed-off-by: NSean Anderson <sean.anderson@seco.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

drivers/core/root.c

@@ -265,7 +265,7 @@ int dm_scan_plat(bool pre_reloc_only)
 static int dm_scan_fdt_node(struct udevice *parent, ofnode parent_node,
 			    bool pre_reloc_only)
 {
-	int ret = 0, err;
+	int ret = 0, err = 0;
 	ofnode node;
 
 	if (!ofnode_valid(parent_node))