regulator: Add docbook for soft start

The docbook for these members is missing. Add them.

Warning(include/linux/regulator/machine.h:147): No description
found for parameter 'soft_start'
Warning(include/linux/regulator/driver.h:197): No description
found for parameter 'set_soft_start'

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

include/linux/regulator/driver.h

@@ -111,6 +111,7 @@ struct regulator_linear_range {
  *               to stabilise after being set to a new value, in microseconds.
  *               The function provides the from and to voltage selector, the
  *               function should return the worst case.
+ * @set_soft_start: Enable soft start for the regulator.
  *
  * @set_suspend_voltage: Set the voltage for the regulator when the system
  *                       is suspended.

include/linux/regulator/machine.h

@@ -87,6 +87,7 @@ struct regulator_state {
  *           applied.
  * @apply_uV: Apply the voltage constraint when initialising.
  * @ramp_disable: Disable ramp delay when initialising or when setting voltage.
+ * @soft_start: Enable soft start so that voltage ramps slowly.
  * @pull_down: Enable pull down when regulator is disabled.
  *
  * @input_uV: Input voltage for regulator when supplied by another regulator.