drivers: usb: nordic: Fix for events when cable is detached

When user disconnects the USB cable, peripheral should be
immediately disabled, howewer a delay may occur when driver
events are processed from a workqueue or higher-priority
thread/ISR is active. This may lead to a fake resume/reset
event (peripheral-specific behavior). This fix drops such
events when cable is detached.

Fixes #13822

Signed-off-by: Paweł Zadrożniak <pawel.zadrozniak@nordicsemi.no>