feat(menu): Return from USB once the host ejects the device

Automatically exit the "USB storage mode" once the connected USB host
ejects card10.

preload/menu.py

@@ -82,7 +82,7 @@ def usb_mode(disp):
         pass
 
     # Wait for any button to be pressed and disable USB storage again
-    while buttons.read() == 0:
+    while buttons.read() == 0 and not os.fs_is_attached():
         pass
 
     os.usbconfig(os.USB_SERIAL)