regulator: fix kernel-doc warnings in header files

Fix kernel-doc warnings in regulator header files:

Warning(..//include/linux/regulator/machine.h:140): No description found for parameter 'ramp_disable'
Warning(..//include/linux/regulator/driver.h:279): No description found for parameter 'linear_ranges'
Warning(..//include/linux/regulator/driver.h:279): No description found for parameter 'n_linear_ranges'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Mark Brown <broonie@linaro.org>