staging: comedi: me4000: use dev->irq to save the irq number

Use the irq variable provided in the comedi_device to save the
irq number and remove it from the private data.

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>