V4L/DVB (6683): Fix DVB compatibility

DVB-S is not supported. Also, there are some QAM6 firmwares for xc3028, but it
is reported that this doesn't work fine.

Thanks to Manu Abraham, Michael Krufky and Patrick Boettcher for their
insights.
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/tuner-xc2028.c

@@ -957,12 +957,14 @@ static int xc2028_set_params(struct dvb_frontend *fe,
 		type |= D2620;
 
 	switch(fe->ops.info.type) {
-	case FE_QPSK:
-		break;
 	case FE_OFDM:
 		bw = p->u.ofdm.bandwidth;
 		break;
 	case FE_QAM:
+		tuner_info("WARN: There are some reports that "
+			   "QAM 6 MHz doesn't work.\n"
+			   "If this works for you, please report by "
+			   "e-mail to: v4l-dvb-maintainer@linuxtv.org\n");
 		bw = BANDWIDTH_6_MHZ;
 		type |= QAM;
 		break;
@@ -970,6 +972,9 @@ static int xc2028_set_params(struct dvb_frontend *fe,
 		bw = BANDWIDTH_6_MHZ;
 		type |= ATSC| D2633;
 		break;
+	/* DVB-S is not supported */
+	default:
+		return -EINVAL;
 	}
 
 	/* FIXME: