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

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

Signed-off-by: Ravishankar Karkala Mallikarjunayya <ravishankar.km@greenturtles.in>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>