[media] rtl2830: implement .read_signal_strength()

static int rtl2830_read_signal_strength(struct dvb_frontend *fe, u16 *strength)

{

	*strength = 0;

	struct rtl2830_priv *priv = fe->demodulator_priv;

	int ret;

	u8 buf[2];

	u16 if_agc_raw, if_agc;

	ret = rtl2830_rd_regs(priv, 0x359, buf, 2);

	if (ret)

		goto err;

	if_agc_raw = (buf[0] << 8 | buf[1]) & 0x3fff;

	if (if_agc_raw & (1 << 9))

		if_agc = -(~(if_agc_raw - 1) & 0x1ff);

	else

		if_agc = if_agc_raw;

	*strength = (u8) (55 - if_agc / 182);

	*strength |= *strength << 8;

	return 0;

err:

	dbg("%s: failed=%d", __func__, ret);

	return ret;

}

static struct dvb_frontend_ops rtl2830_ops;