[media] cxd2820r: improve IF frequency setting

Use 64-bit calculation.

Return error if tuner does not provide get_if_frequency() callback.
All currently used tuners has it.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/dvb-frontends/cxd2820r_priv.h

@@ -34,6 +34,8 @@ struct reg_val_mask {
 	u8  mask;
 };
 
+#define CXD2820R_CLK 41000000
+
 struct cxd2820r_priv {
 	struct i2c_adapter *i2c;
 	struct dvb_frontend fe;