staging: comedi: pcmuio: refactor interrupt_pcmuio()

Refactor this function into two new functions in order to reduce the indent
levels and clean up the ugly line breaks that, unsuccessfully, try to keep
the lines < 80 chars.

The first function handles the irq for a specific asic.

The second function handles the irq for a specific subdevice that is
associated with the asic.

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>