kernel-doc: fix new warnings in driver-core

Fix new kernel-doc warnings:

Warning(drivers/base/bus.c:925): No description found for parameter 'key'
Warning(drivers/base/bus.c:1241): No description found for parameter 'subsys'
Warning(drivers/base/bus.c:1241): No description found for parameter 'groups'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>