staging: comedi: pcl812: tidy up the irq support in pcl812_attach()

Tidy up the code that does the request_irq().

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>