regulator: fix kernel-doc warnings in drivers/regulator/core.c

Fix regulator kernel-doc warnings:

Warning(drivers/regulator/core.c:2308): No description found for parameter 'rdev'
Warning(drivers/regulator/core.c:2308): Excess function parameter 'regulator' description in 'regulator_set_voltage_time_sel'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc:	Liam Girdwood <lrg@ti.com>
Cc:	Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>