iio: light: us5182d: Fix formatting in kerneldoc function block

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

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

 drivers/iio/light/us5182d.c:457: warning: Function parameter or member 'data' not described in 'us5182d_update_dark_th'
 drivers/iio/light/us5182d.c:457: warning: Function parameter or member 'index' not described in 'us5182d_update_dark_th'
 drivers/iio/light/us5182d.c:479: warning: Function parameter or member 'data' not described in 'us5182d_apply_scale'
 drivers/iio/light/us5182d.c:479: warning: Function parameter or member 'index' not described in 'us5182d_apply_scale'

Cc: Adriana Reus <adriana.reus@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>