iio: st_sensors: correct kernel-doc issues

iio: st_sensors: correct kernel-doc issues

Use the proper kernel-doc format and struct member names to avoid
kernel-doc warnings:

Warning: include/linux/iio/common/st_sensors.h:184 struct member 'int1'
 not described in 'st_sensor_data_ready_irq'
Warning: ../include/linux/iio/common/st_sensors.h:184 struct member 'int2'
 not described in 'st_sensor_data_ready_irq'
Warning: ../include/linux/iio/common/st_sensors.h:184 struct member
 'stat_drdy' not described in 'st_sensor_data_ready_irq'
Warning: ../include/linux/iio/common/st_sensors.h:184 struct member 'ig1'
 not described in 'st_sensor_data_ready_irq'
Warning: ../include/linux/iio/common/st_sensors.h:219 struct member
 'num_ch' not described in 'st_sensor_settings'
Warning: ../include/linux/iio/common/st_sensors.h:263 struct member
 'num_data_channels' not described in 'st_sensor_data'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>