USB: fix aircable.c: inconsequent NULL checking

USB: fix aircable.c: inconsequent NULL checking

> 2006/11/11, Adrian Bunk <bunk@stusta.de>:
> > The Coverity checker spotted the following in
> > drivers/usb/serial/aircable.c:
> >
> > <--  snip  -->
> >
> > ...
> > static void aircable_read(void *params)
> > {
> > ...

Hi everyone,
Sorry for the long time response but here is the patch, I think this way should
work, if anyone has any suggestion let me know. What I do now is, in case I
don't have the tty available I reschedule the work, I have tried it and it
works with no problem, I even tried removing the device, and didn't find
anything strange.

Signed-off-by: Naranjo Manuel <naranjo.manuel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>