staging: comedi: cb_pcidas: consolidate interrupt clear code

The analog output and analog input interrupts are currently cleared
as they are handled. Refactor the code to gather all the bits needed
to clear the interrupts and do it once at the end of the interrupt
handler.

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>