iio/adc: ingenic: Fix battery VREF for JZ4770 SoC

The reference voltage for the battery is clearly marked as 1.2V in the
programming manual. With this fixed, the battery channel now returns
correct values.

Fixes: a515d648 ("IIO: Ingenic JZ47xx: Add support for JZ4770 SoC ADC.")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Artur Rojek <contact@artur-rojek.eu>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20201104192843.67187-1-paul@crapouillou.netSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ingenic-adc.c

@@ -71,7 +71,7 @@
 #define JZ4725B_ADC_BATTERY_HIGH_VREF_BITS	10
 #define JZ4740_ADC_BATTERY_HIGH_VREF		(7500 * 0.986)
 #define JZ4740_ADC_BATTERY_HIGH_VREF_BITS	12
-#define JZ4770_ADC_BATTERY_VREF			6600
+#define JZ4770_ADC_BATTERY_VREF			1200
 #define JZ4770_ADC_BATTERY_VREF_BITS		12
 
 #define JZ_ADC_IRQ_AUX			BIT(0)