iio: adc: vf610_adc: Fix VALT selection value for REFSEL bits

In order to select the alternate voltage reference pair (VALTH/VALTL), the
right value for the REFSEL field in the ADCx_CFG register is "01", leading
to 0x800 as register mask. See section 8.2.6.4 in the reference manual[1].

[1] http://www.nxp.com/docs/en/reference-manual/VFXXXRM.pdf

Fixes: a7754276 ("iio:adc:imx: add Freescale Vybrid vf610 adc driver")
Signed-off-by: Stefan-Gabriel Mirea <stefan-gabriel.mirea@nxp.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/vf610_adc.c

@@ -77,7 +77,7 @@
 #define VF610_ADC_ADSTS_MASK		0x300
 #define VF610_ADC_ADLPC_EN		0x80
 #define VF610_ADC_ADHSC_EN		0x400
-#define VF610_ADC_REFSEL_VALT		0x100
+#define VF610_ADC_REFSEL_VALT		0x800
 #define VF610_ADC_REFSEL_VBG		0x1000
 #define VF610_ADC_ADTRG_HARD		0x2000
 #define VF610_ADC_AVGS_8		0x4000