Staging: comedi: fix initialise statics to 0 or NULL issue in pcl816.c

This is a patch to the pcl816.c file that fixes up a initialise statics to 0 or NULL
warning found by the checkpatch.pl tool.

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