media: cxd2880: remove unused vars

drivers/media/dvb-frontends/cxd2880/cxd2880_top.c: In function ‘cxd2880_set_ber_per_period_t’:
drivers/media/dvb-frontends/cxd2880/cxd2880_top.c:677:34: warning: variable ‘c’ set but not used [-Wunused-but-set-variable]
  struct dtv_frontend_properties *c;
                                  ^
drivers/media/dvb-frontends/cxd2880/cxd2880_top.c: In function ‘cxd2880_set_ber_per_period_t2’:
drivers/media/dvb-frontends/cxd2880/cxd2880_top.c:790:34: warning: variable ‘c’ set but not used [-Wunused-but-set-variable]
  struct dtv_frontend_properties *c;
                                  ^
drivers/media/dvb-frontends/cxd2880/cxd2880_top.c: In function ‘cxd2880_get_frontend’:
drivers/media/dvb-frontends/cxd2880/cxd2880_top.c:1799:23: warning: variable ‘priv’ set but not used [-Wunused-but-set-variable]
  struct cxd2880_priv *priv = NULL;
                       ^~~~

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>