Fixes the following warnings:
drivers/media/dvb-frontends/drx39xyj/drxj.c:1679:65: warning: Using plain integer as NULL pointer
drivers/media/dvb-frontends/drx39xyj/drxj.c:1679:71: warning: Using plain integer as NULL pointer
drivers/media/dvb-frontends/drx39xyj/drxj.c:1681:52: warning: Using plain integer as NULL pointer
drivers/media/dvb-frontends/drx39xyj/drxj.c:1681:58: warning: Using plain integer as NULL pointer