AD4851_REG_CHX_OFFSET_MID
#define AD4851_REG_CHX_OFFSET_MSB(ch) (AD4851_REG_CHX_OFFSET_MID(ch) + 0x01)
ret = regmap_read(st->regmap, AD4851_REG_CHX_OFFSET_MID(ch), &mid);
ret = regmap_write(st->regmap, AD4851_REG_CHX_OFFSET_MID(ch), buf[1]);