iio: dac: ad5360: Fix kerneldoc attribute formatting for 'lock'
Kerneldoc expects attributes/parameters to be in '@*.: ' format.
Fixes the following W=1 kernel build warning(s):
drivers/iio/dac/ad5360.c:89: warning: Function parameter or member 'lock' not described in 'ad5360_state'
Cc: Michael Hennerich <Michael.Hennerich@analog.com> Signed-off-by: Lee Jones <lee.jones@linaro.org> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>