[media] drx-j: get rid of some unused vars

As reported when compiled with W=1:

drivers/media/dvb-frontends/drx39xyj/drxj.c: In function ‘ctrl_set_channel’:
drivers/media/dvb-frontends/drx39xyj/drxj.c:10340:26: warning: variable ‘common_attr’ set but not used [-Wunused-but-set-variable]
  struct drx_common_attr *common_attr = NULL;
                          ^
drivers/media/dvb-frontends/drx39xyj/drxj.c:10336:6: warning: variable ‘intermediate_freq’ set but not used [-Wunused-but-set-variable]
  s32 intermediate_freq = 0;

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