staging: comedi: ni_mio_common: remove deadcode in ni_cdio_cmdtest()

Reported-by: coverity (CID 142967)
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>