kernel-doc: fix new warning in regulator core

Fix new kernel-doc warning:

Warning(drivers/regulator/core.c:2741): No description found for parameter 'of_node'

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