iio: imu: kmx61: Fix formatting in kerneldoc function headers

Kerneldoc expects attributes/parameters to be in '@*.: ' format.

Fixes the following W=1 kernel build warning(s):

 drivers/iio/imu/kmx61.c:327: warning: Function parameter or member 'data' not described in 'kmx61_set_mode'
 drivers/iio/imu/kmx61.c:327: warning: Function parameter or member 'mode' not described in 'kmx61_set_mode'
 drivers/iio/imu/kmx61.c:327: warning: Function parameter or member 'device' not described in 'kmx61_set_mode'
 drivers/iio/imu/kmx61.c:327: warning: Function parameter or member 'update' not described in 'kmx61_set_mode'
 drivers/iio/imu/kmx61.c:731: warning: Function parameter or member 'data' not described in 'kmx61_set_power_state'
 drivers/iio/imu/kmx61.c:731: warning: Function parameter or member 'on' not described in 'kmx61_set_power_state'
 drivers/iio/imu/kmx61.c:731: warning: Function parameter or member 'device' not described in 'kmx61_set_power_state'

Cc: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>