Staging: comedi: usbdux: buffer overflow error handling

These changes guarantee that the URBs are not resubmitted in case of a
comedi buffer overflow.  Otherwise this runs in the background even when
the userspace program has terminated.

From: Bernd Porr <BerndPorr@f2s.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>