These changes are unrelated except I ran into them all at once:

- Fixes an oops from a partial hub_configure() clean; let
   hub_disconnect() do the whole thing, simpler.

- Since I was there, modify that routine's err() messages
   to use dev_err().  Then eliminate a redundant diagnostic
   in hub_probe(), and merge the "bad descriptor" cases into
   one diagnostic.  Saves a few hundred rodata bytes, and
   the messages now say what hub's involved.

- Unlink fixes:  if lower level code reports a submit error,
   make sure the urb gets unlinked from the device's urb_list;
   and report "it's already being unlinked" as -EBUSY so callers
   can do something smarter than wonder "what did I do wrong".