iio: adc: adi-axi-adc: fix typo in doc-string

The channels are of type iio_chan_spec, not axi_adc_chan_spec. They were in
some earlier version, but forgot to rename in the doc-string.

Fixes: ef040706 ("iio: adc: adi-axi-adc: add support for AXI ADC IP core")
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210219090134.48057-1-alexandru.ardelean@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

include/linux/iio/adc/adi-axi-adc.h

@@ -15,7 +15,7 @@ struct iio_chan_spec;
  * struct adi_axi_adc_chip_info - Chip specific information
  * @name		Chip name
  * @id			Chip ID (usually product ID)
- * @channels		Channel specifications of type @struct axi_adc_chan_spec
+ * @channels		Channel specifications of type @struct iio_chan_spec
  * @num_channels	Number of @channels
  * @scale_table		Supported scales by the chip; tuples of 2 ints
  * @num_scales		Number of scales in the table