staging: comedi: pcmmio: tidy up the irq request

The for () loop that does the request_irq() in this driver is a bit of
an overkill. The code appears to have been copied from the pcmuio driver
which supports boards with 1 or 2 ASIC devices. The board supported by
this driver only has 1 ASIC.

Simplify the code and store the irq number in the comedi_device. This
allows the core to automatically do the free_irq() when the driver is
detached.

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>