staging: comedi: me4000: remove unnecessary check in the irq handler

The sanity check of the irq is not necessary. If it _is_ wrong we have
bigger problems in the kernel...

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>