staging: comedi: ni_tio: tidy up ni_660x_set_second_gate()

Rename some of the local vars and tidy up this function to fix to
fix a couple > 80 char line issues.

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>