USB: devio: fix a condition in async_completed()

Static checkers complain that the current condition is never true.  It
seems pretty likely that it's a typo and "URB" was intended instead of
"USB".

Fixes: 3d97ff63 ('usbdevfs: Use scatter-gather lists for large bulk transfers')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>