staging: comedi: adl_pci7230: remove the private data

The private data is no longer needed by this driver. Remove the
struct, devpriv macro, and the allocation.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>