driver core: Avoid NULL pointer dereferences in device_is_bound()

If device_is_bound() is called on a device that's not been registered
yet, it will attepmt to dereference dev->p which is NULL, so avoid
that by checking dev->p in there against NULL.

Fixes: 6b9cb42752da "device core: add device_is_bound()"
Reported-and-tested-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 0499421..c4da2df 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -234,7 +234,7 @@
  */
 bool device_is_bound(struct device *dev)
 {
-	return klist_node_attached(&dev->p->knode_driver);
+	return dev->p && klist_node_attached(&dev->p->knode_driver);
 }
 
 static void driver_bound(struct device *dev)