backlight: fix backlight_device_register compile failures

Fix breakage from commit 519ab5f2be65b72cf12ae99c89752bbe79b44df6 which
didn't update all references to backlight_device_register causing
compile failures.

Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Len Brown <len.brown@intel.com>

diff --cc drivers/video/backlight/corgi_bl.c
Simple merge

diff --cc drivers/video/backlight/hp680_bl.c
Simple merge

diff --cc drivers/video/backlight/locomolcd.c
Simple merge