iio: adc: qcom-pm8xxx-xoadc: Demote standard comment block and supply missing description

Kerneldoc is only suitable for documenting functions and struct/enums.

Fixes the following W=1 kernel build warning(s):

 drivers/iio/adc/qcom-pm8xxx-xoadc.c:133: warning: Excess function parameter 'PM8XXX_CHANNEL_INTERNAL' description in 'PM8XXX_CHANNEL_INTERNAL'
 drivers/iio/adc/qcom-pm8xxx-xoadc.c:133: warning: Excess function parameter 'PM8XXX_CHANNEL_125V' description in 'PM8XXX_CHANNEL_INTERNAL'
 drivers/iio/adc/qcom-pm8xxx-xoadc.c:133: warning: Excess function parameter 'PM8XXX_CHANNEL_INTERNAL_2' description in 'PM8XXX_CHANNEL_INTERNAL'
 drivers/iio/adc/qcom-pm8xxx-xoadc.c:133: warning: Excess function parameter 'PM8XXX_CHANNEL_MUXOFF' description in 'PM8XXX_CHANNEL_INTERNAL'
 drivers/iio/adc/qcom-pm8xxx-xoadc.c:412: warning: Function parameter or member 'variant' not described in 'pm8xxx_xoadc'

Cc: Andy Gross <agross@kernel.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-arm-msm@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/qcom-pm8xxx-xoadc.c

@@ -120,7 +120,7 @@
 #define ADC_ARB_USRP_DATA0			0x19D
 #define ADC_ARB_USRP_DATA1			0x19C
 
-/**
+/*
  * Physical channels which MUST exist on all PM variants in order to provide
  * proper reference points for calibration.
  *
@@ -388,6 +388,7 @@ struct pm8xxx_chan_info {
  * struct pm8xxx_xoadc - state container for the XOADC
  * @dev: pointer to device
  * @map: regmap to access registers
+ * @variant: XOADC variant characteristics
  * @vref: reference voltage regulator
  * characteristics of the channels, and sensible default settings
  * @nchans: number of channels, configured by the device tree