usb: better error handling in usb_port_suspend

- disable remote wakeup only if it was enabled
- refuse to autosuspend if remote wakeup fails to be enabled

Signed-off-by: Oliver Neukum <oliver@neukum.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>