Staging: comedi: fix initialise statics to 0 or NULL issue in ni_daq_dio24.c

This is a patch to the ni_daq_dio24.c file that fixes up a initialise
statics to 0 or NULL warning found by the checkpatch.pl tool.
Signed-off-by: NRavishankar Karkala Mallikarjunayya <ravishankar.km@greenturtles.in>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/comedi/drivers/ni_daq_dio24.c

@@ -52,7 +52,7 @@ the PCMCIA interface.
 #include <pcmcia/cisreg.h>
 #include <pcmcia/ds.h>
 
-static struct pcmcia_device *pcmcia_cur_dev = NULL;
+static struct pcmcia_device *pcmcia_cur_dev;
 
 #define DIO24_SIZE 4		/*  size of io region used by board */