USB: debugging code shouldn't alter control flow

People have complained that debugging code shouldn't alter the flow of
control; it should restrict itself to printing out warnings and error
messages.  Bowing to popular opinion, this patch (as1518) changes the
debugging checks in usb_submit_urb() to follow this guideline.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Keith Packard <keithp@keithp.com>
CC: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>