staging: comedi: addi_apci_2032: tidy up cmd use in apci2032_interrupt()

Use a local variable for the comedi_cmd and tidy up this function a bit.

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>