[PATCH] USB: Important bugfix for UHCI list management code

[PATCH] USB: Important bugfix for UHCI list management code

A major bug in the UHCI driver turned up recently.  Thanks to a lot of
help from Simone Gotti it was identified and fixed late last week.  It
turned out to be entirely my fault -- a previous patch had introduced two
(!) errors.  (A combination of carelessness and a nasty thinko, and
somehow it passed the regression tests...)

Anyway, it's entirely possible that many of the problems people have been
seeing are caused by that bug.  This patch is the solution.