regulator: pwm-regulator: Demote kerneldoc header to standard comment

This particular comment doesn't have anything to do with documenting
functions or data structures.  Instead it is used as a section header.

Fixes W=1 warning:

 drivers/regulator/pwm-regulator.c:55: warning: Function parameter or member 'rdev' not described in 'pwm_regulator_init_state'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200626065738.93412-4-lee.jones@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>