Staging: comedi: fix line over 80 character issue in rtd520.c

This is a patch to the rtd520.c file that fixes up a  warning: line over 80 character found by the checkpatch.pl tool

Signed-off-by: Ravishankar <ravishankarkm32@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>