[PATCH] USB: UHCI: fix obscure bug in enqueue()

This patch (as676) fixes a small bug in uhci-hcd's enqueue routine.  When
an URB is unlinked or gets an error and the completion handler queues
another URB for the same endpoint, the queue shouldn't be allowed to start
up again until the handler returns.  Not even if the new URB is the only
one on its queue.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>