[media] m88ds3103: fix bug on .set_tone()

Band switching didn't worked always reliably as there was one
register bit set wrong.

Thanks to Robert Schlabbach for pointing this bug and solution.
Reported-by: NRobert Schlabbach <Robert.Schlabbach@gmx.net>
Signed-off-by: NAntti Palosaari <crope@iki.fi>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/dvb-frontends/m88ds3103.c

@@ -944,7 +944,7 @@ static int m88ds3103_set_tone(struct dvb_frontend *fe,
 	switch (fe_sec_tone_mode) {
 	case SEC_TONE_ON:
 		tone = 0;
-		reg_a1_mask = 0x87;
+		reg_a1_mask = 0x47;
 		break;
 	case SEC_TONE_OFF:
 		tone = 1;