[PATCH] USB: Usbcore: Don't try to delete unregistered interfaces
This patch handles a rarely-encountered failure mode in usbcore. It's
legal for device_add to fail (although now it happens even more rarely
than before since failure to bind a driver is no longer fatal). So when
we destroy the interfaces in a configuration, we shouldn't try to delete
ones which weren't successfully registered. Also, failure to register an
interface shouldn't be fatal either -- I think; you may disagree about
this part of the patch.