staging: comedi: amplc_dio200: remove dio200_common_detach()

This exported function just does a free_irq() to release the interrupt
handler for the legacy and PCI dio200 drivers.

The legacy driver also calls comedi_legacy_detach() which would also
do the free_irq(). For that driver the just use comedi_legacy_detach()
directly for the (*detach).

For the PCI driver, add the free_irq() to the private (*datach) function.

Remove the, then unused, dio200_common_detach() function.

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>