iio: proximity: rfd77402: Document device private data structure

Add kernel-doc style comments for struct rfd77402_data to describe
the purpose of each member.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Shrikant Raskar <raskar.shree97@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: embedded-essentials

drivers/iio/proximity/rfd77402.c

@@ -77,9 +77,13 @@ static const struct {
 	{RFD77402_HFCFG_3,	0x45d4},
 };
 
+/**
+ * struct rfd77402_data - device-specific data for the RFD77402 sensor
+ * @client: I2C client handle
+ * @lock: mutex to serialize sensor reads
+ */
 struct rfd77402_data {
 	struct i2c_client *client;
-	/* Serialize reads from the sensor */
 	struct mutex lock;
 };