[media] drx-j: Don't use 0 as NULL

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

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>