dm: usb: Fix "usb tree" output

last_child was abused by the old usb code to first store 1 if the
usb_device was not the root of the usb tree, and then later on re-used
to store whether or not the usb_device is actually the last child.

The dm-usb code was always setting it to actually reflect the last-child
status which is wrong for the last child leading to output like this:

USB device tree:
  1  Hub (12 Mb/s, 100mA)
  |  ALCOR USB Hub 2.0
  |
  | 2  Mass Storage (12 Mb/s, 100mA)
  |    USB Flash Disk 4C0E960F
  |
  +-3  Human Interface (1.5 Mb/s, 100mA)
       SINO WEALTH USB Composite Device

Instead of this:

USB device tree:
  1  Hub (12 Mb/s, 100mA)
  |  ALCOR USB Hub 2.0
  |
  +-2  Mass Storage (12 Mb/s, 100mA)
  |    USB Flash Disk 4C0E960F
  |
  +-3  Human Interface (1.5 Mb/s, 100mA)
       SINO WEALTH USB Composite Device

This commit fixes this by first checking that the device is not root,
and then setting last_child. This commit also updates the old code to not
abuse the last_child variable to store the root check result.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Simon Glass <sjg@chromium.org>

common/cmd_usb.c

@@ -355,12 +355,12 @@ static void usb_show_tree_graph(struct usb_device *dev, char *pre)
 #endif
 	/* check if we are the last one */
 #ifdef CONFIG_DM_USB
-	last_child = device_is_last_sibling(dev->dev);
+	/* Not the root of the usb tree? */
+	if (device_get_uclass_id(dev->dev->parent) != UCLASS_USB) {
+		last_child = device_is_last_sibling(dev->dev);
 #else
-	last_child = (dev->parent != NULL);
-#endif
-	if (last_child) {
-#ifndef CONFIG_DM_USB
+	if (dev->parent != NULL) { /* not root? */
+		last_child = 1;
 		for (i = 0; i < dev->parent->maxchild; i++) {
 			/* search for children */
 			if (dev->parent->children[i] == dev) {