USB: reorganize urb->status use in sl811-hcd

This patch (as976) reorganizes the way sl811-hcd sets urb->status.  It
now keeps the information in a local variable until the last moment.

The patch also improves the handling of faults during the status stage
of a control transfer, since it no longer needs to retain the error
information from the earlier stages.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>