USB: serial: digi_acceleport: fix hard lockup on disconnect

In the Linux kernel, the following vulnerability has been resolved: USB: serial: digi_acceleport: fix hard lockup on disconnect If submitting the OOB write urb fails persistently (e.g if the device is being disconnected) the driver would loop indefinitely with interrupts disabled. Check for urb submission errors when sending OOB commands to avoid hanging if, for example, open(), set_termios() or close() races with a physical disconnect. This is issue was flagged by Sashiko when reviewing an unrelated change to the driver.