iio: st_sensors: Describe function parameters in kernel-doc

Kernel documentation script complains that some of the function parameters
are not described:

.../common/st_sensors/st_sensors_trigger.c:29: warning: Function parameter or member 'indio_dev' not described in 'st_sensors_new_samples_available'
.../common/st_sensors/st_sensors_trigger.c:29: warning: Function parameter or member 'sdata' not described in 'st_sensors_new_samples_available'

Describe function parameters where it's appropriate.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/common/st_sensors/st_sensors_trigger.c

@@ -19,6 +19,9 @@
 
 /**
  * st_sensors_new_samples_available() - check if more samples came in
+ * @indio_dev: IIO device reference.
+ * @sdata: Sensor data.
+ *
  * returns:
  * 0 - no new samples available
  * 1 - new samples available