staging: comedi: comedi_parport: remove 'enable_irq' from private data

The enabled state of the interrupt can be checked by reading the control
register.

Remove 'enabled_irq' from the private data.

Since the private data is now empty, remove it completely and remove the
allocation of it in parport_attach().

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>