USB: gadget: android: check for null _android_dev in android_register_function()

This fixes a load ordering issue that occurred if a function driver loads before
the android gadget driver is initialized.

Signed-off-by: Mike Lockwood <lockwood@android.com>
diff --git a/drivers/usb/gadget/android.c b/drivers/usb/gadget/android.c
index 70e48ac..3c4d44d 100644
--- a/drivers/usb/gadget/android.c
+++ b/drivers/usb/gadget/android.c
@@ -313,7 +313,7 @@
 	/* bind our functions if they have all registered
 	 * and the main driver has bound.
 	 */
-	if (dev->config && _registered_function_count == dev->num_functions)
+	if (dev && dev->config && _registered_function_count == dev->num_functions)
 		bind_functions(dev);
 }