usb(4): Don't skip calling uhub_explore_sub() even on HUB port errors.

This should fix an issue where the "udev->re_enumerate_wait" field never gets
processed and reset. In this case usbconfig will wait forever and never return.

Sponsored by: NVIDIA Networking

(cherry picked from commit c7cd6f809d2ce6b7d331717c31ce51c631ae00d7)