This patch updates the cpia driver.

Additionally to the usual adoptions to the videodev changes done in all
drivers this patch has a few more changes:

 - some cleanups in the drivers open() function.
 - Use file->private_data to keep a pointer to the drivers private
   data.  This allows to unregister the device unconditionally in
   disconnect(), which in turn fixes some small races in case the
   device is unplugged while in use.