trivial: NULL noise: drivers/media/dvb/frontends/drx397xD_fw.h

Fix this sparse warnings:
  drivers/media/dvb/frontends/drx397xD_fw.h:21:2: warning: Using plain integer as NULL pointer
  drivers/media/dvb/frontends/drx397xD_fw.h:22:2: warning: Using plain integer as NULL pointer

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>