[media] si2157.c: fix frequency range

According with:
	https://www.silabs.com/Support%20Documents/TechnicalDocs/Si2157-short.pdf

The RF input frequency range of this demod is from 42MHz to 870 MHz.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/tuners/si2157.c

@@ -364,8 +364,8 @@ static int si2157_get_if_frequency(struct dvb_frontend *fe, u32 *frequency)
 static const struct dvb_tuner_ops si2157_ops = {
 	.info = {
 		.name           = "Silicon Labs Si2146/2147/2148/2157/2158",
-		.frequency_min  = 55000000,
-		.frequency_max  = 862000000,
+		.frequency_min  = 42000000,
+		.frequency_max  = 870000000,
 	},
 
 	.init = si2157_init,