staging: comedi: pcm3724: use default (*io) callback from 8255 module

The private (*io) callback used by this driver is identical to the
default one provided by the 8255 module. Use the default one instead.

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