[media] saa7164: fix sparse warning

drivers/media/pci/saa7164/saa7164-i2c.c:45:33: warning: Using plain integer as NULL pointer

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Steven Toth <stoth@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>