this adds error handling to the open method of the cdc acm driver.
The change set is relative to my last patch rewriting probe.
  - add error handling to open method
Signed-off-by: Oliver Neukum <oliver@neukum.name>
Signed-off-by: Vojtech Pavlik <vojtech@suse.cz>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>