staging: iio: ad2s1200: Add kernel docs to driver state

Add missing kernel docs to the ad2s1200 driver state.
Signed-off-by: David Veenstra <davidjulianveenstra@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/resolver/ad2s1200.c

@@ -32,6 +32,14 @@
 /* clock period in nano second */
 #define AD2S1200_TSCLK	(1000000000 / AD2S1200_HZ)
 
+/**
+ * struct ad2s1200_state - driver instance specific data.
+ * @lock:	protects both the GPIO pins and the rx buffer.
+ * @sdev:	spi device.
+ * @sample:	GPIO pin SAMPLE.
+ * @rdvel:	GPIO pin RDVEL.
+ * @rx:		buffer for spi transfers.
+ */
 struct ad2s1200_state {
 	struct mutex lock;
 	struct spi_device *sdev;