[media] cxd2820r_c: fix if_ctl calculation

fixes tuning for DVB-C

Signed-off-by: Evgeny Plehov <EvgenyPlehov@ukr.net>
Reviewed-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/dvb-frontends/cxd2820r_c.c

@@ -78,7 +78,7 @@ int cxd2820r_set_frontend_c(struct dvb_frontend *fe)
 
 	num = if_freq / 1000; /* Hz => kHz */
 	num *= 0x4000;
-	if_ctl = cxd2820r_div_u64_round_closest(num, 41000);
+	if_ctl = 0x4000 - cxd2820r_div_u64_round_closest(num, 41000);
 	buf[0] = (if_ctl >> 8) & 0x3f;
 	buf[1] = (if_ctl >> 0) & 0xff;