regulator: fix header file missing kernel-doc

Fix regulator/driver.h missing kernel-doc:

Warning(linux-next-20090120//include/linux/regulator/driver.h:108): No description found for parameter 'get_status'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
cc: Liam Girdwood <lrg@slimlogic.co.uk>
cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>